core: refactor seek_chapter() function

Makes it easier to understand... maybe. It's still pretty strange how
this function may either queue the seek or seek immediately. The way
it actually works doesn't change, queuing the seek is just moved into
the function.

Also add a execute_queued_seek() function, which resets the queue state
correctly.

core/command.c

@@ -350,14 +350,11 @@ static int mp_property_chapter(m_option_t *prop, int action, void *arg,
     case M_PROPERTY_SET: ;
         int step_all = *(int *)arg - chapter;
         chapter += step_all;
-        double next_pts = 0;
-        queue_seek(mpctx, MPSEEK_NONE, 0, 0);
-        chapter = seek_chapter(mpctx, chapter, &next_pts);
-        if (chapter >= 0) {
-            if (next_pts > -1.0)
-                queue_seek(mpctx, MPSEEK_ABSOLUTE, next_pts, 0);
-        } else if (step_all > 0)
+        if (chapter >= get_chapter_count(mpctx) && step_all > 0) {
             mpctx->stop_play = PT_NEXT_ENTRY;
+        } else {
+            mp_seek_chapter(mpctx, chapter);
+        }
         return M_PROPERTY_OK;
     }
     return M_PROPERTY_NOT_IMPLEMENTED;

core/mp_core.h

@@ -303,7 +303,7 @@ void unpause_player(struct MPContext *mpctx);
 void add_step_frame(struct MPContext *mpctx, int dir);
 void queue_seek(struct MPContext *mpctx, enum seek_type type, double amount,
                 int exact);
-int seek_chapter(struct MPContext *mpctx, int chapter, double *seek_pts);
+bool mp_seek_chapter(struct MPContext *mpctx, int chapter);
 double get_time_length(struct MPContext *mpctx);
 double get_start_time(struct MPContext *mpctx);
 double get_current_time(struct MPContext *mpctx);

core/mplayer.c

@@ -3113,6 +3113,14 @@ void queue_seek(struct MPContext *mpctx, enum seek_type type, double amount,
     abort();
 }
 
+static void execute_queued_seek(struct MPContext *mpctx)
+{
+    if (mpctx->seek.type) {
+        seek(mpctx, mpctx->seek, false);
+        mpctx->seek = (struct seek_params){0};
+    }
+}
+
 double get_time_length(struct MPContext *mpctx)
 {
     struct demuxer *demuxer = mpctx->demuxer;
@@ -3262,33 +3270,42 @@ int get_chapter_count(struct MPContext *mpctx)
     return 0;
 }
 
-int seek_chapter(struct MPContext *mpctx, int chapter, double *seek_pts)
+// Seek to a given chapter. Tries to queue the seek, but might seek immediately
+// in some cases. Returns success, no matter if seek is queued or immediate.
+bool mp_seek_chapter(struct MPContext *mpctx, int chapter)
 {
-    mpctx->last_chapter_seek = -2;
-    if (mpctx->chapters) {
-        if (chapter >= mpctx->num_chapters)
-            return -1;
-        if (chapter < 0)
-            chapter = 0;
-        *seek_pts = mpctx->chapters[chapter].start;
-        mpctx->last_chapter_seek = chapter;
-        mpctx->last_chapter_pts = *seek_pts;
-        return chapter;
-    }
+    int num = get_chapter_count(mpctx);
+    if (num == 0)
+        return false;
+    if (chapter < 0 || chapter >= num)
+        return false;
 
-    if (mpctx->master_demuxer) {
-        int res = demuxer_seek_chapter(mpctx->master_demuxer, chapter, seek_pts);
+    mpctx->last_chapter_seek = -2;
+
+    double pts;
+    if (mpctx->chapters) {
+        pts = mpctx->chapters[chapter].start;
+        goto do_seek;
+    } else if (mpctx->master_demuxer) {
+        int res = demuxer_seek_chapter(mpctx->master_demuxer, chapter, &pts);
         if (res >= 0) {
-            if (*seek_pts == -1)
-                seek_reset(mpctx, true, true);  // for DVD
-            else {
-                mpctx->last_chapter_seek = res;
-                mpctx->last_chapter_pts = *seek_pts;
+            if (pts == -1) {
+                // for DVD/BD - seek happened via stream layer
+                seek_reset(mpctx, true, true);
+                mpctx->seek = (struct seek_params){0};
+                return true;
             }
+            chapter = res;
+            goto do_seek;
         }
-        return res;
     }
-    return -1;
+    return false;
+
+do_seek:
+    queue_seek(mpctx, MPSEEK_ABSOLUTE, pts, 0);
+    mpctx->last_chapter_seek = chapter;
+    mpctx->last_chapter_pts = pts;
+    return true;
 }
 
 static void update_avsync(struct MPContext *mpctx)
@@ -3772,10 +3789,7 @@ static void run_playloop(struct MPContext *mpctx)
         }
     }
 
-    if (mpctx->seek.type) {
-        seek(mpctx, mpctx->seek, false);
-        mpctx->seek = (struct seek_params){ 0 };
-    }
+    execute_queued_seek(mpctx);
 }
 
 
@@ -4363,23 +4377,19 @@ goto_enable_cache: ;
     mpctx->playing_msg_shown = false;
     mpctx->paused = false;
     mpctx->paused_for_cache = false;
+    mpctx->seek = (struct seek_params){ 0 };
 
     // If there's a timeline force an absolute seek to initialize state
     double startpos = rel_time_to_abs(mpctx, opts->play_start, -1);
     if (startpos != -1 || mpctx->timeline) {
         queue_seek(mpctx, MPSEEK_ABSOLUTE, startpos, 0);
-        seek(mpctx, mpctx->seek, false);
+        execute_queued_seek(mpctx);
     }
     if (opts->chapterrange[0] > 0) {
-        double pts;
-        if (seek_chapter(mpctx, opts->chapterrange[0] - 1, &pts) >= 0
-            && pts > -1.0) {
-            queue_seek(mpctx, MPSEEK_ABSOLUTE, pts, 0);
-            seek(mpctx, mpctx->seek, false);
-        }
+        if (mp_seek_chapter(mpctx, opts->chapterrange[0] - 1))
+            execute_queued_seek(mpctx);
     }
 
-    mpctx->seek = (struct seek_params){ 0 };
     get_relative_time(mpctx); // reset current delta
 
     if (mpctx->opts.pause)