command: make sure to redraw on overlay commands

When overlay-add etc. is run, make sure the playlop is rerun so that it
considers actually redrawing the screen.

(I considered making the OSD code generally wakeup the player, but that
will probably lead to redundant wakeups, so I didn't bother.)

Fixes #5431.

player/command.c

@@ -4586,6 +4586,7 @@ done:
     }
 
     osd_set_external2(mpctx->osd, new);
+    mp_wakeup_core(mpctx);
     cmd->overlay_osd_current = overlay_next;
 }