vo_gpu: fix display corruption with window screenshots

The "screenshot window" command (ctrl+s by default) somehow broke video
colors with --gpu-api=vulkan --profile=gpu-hq when playback was paused.
I don't know the cause, but the rest of the code seems to imply
gl_video_reset_surfaces() needs to be called manually to flush some
caches, and it fixes the issue, so I assume there's no great mystery
here.

video/out/gpu/video.c

@@ -3458,6 +3458,7 @@ done:
     talloc_free(nframe);
     ra_tex_free(p->ra, &target);
     gl_video_resize(p, &old_src, &old_dst, &old_osd);
+    gl_video_reset_surfaces(p);
     if (!ok)
         TA_FREEP(&res);
     args->res = res;