playloop: unset last_chapter_flag when queueing non-chapter seeks

This fixes a race condition where if a non-chapter seek is queued
immediately after a chapter seek is queued, the chapter property may
become unavailable until a new file is loaded.

If multiple seeks are queued within the same playloop iteration, only
the last seek is executed. Because the chapter seek is never executed,
last_chapter_flag remains set and last_chapter_seek becomes -2, which
causes get_current_chapter to return -2, which makes the chapter
property unavailable.

Unset this (and also last_chapter_seek) immediately rather than
wait for seek execution, like chapter seeks set these immediately.

Author: layercak3

player/playloop.c

@@ -279,8 +279,6 @@ static void mp_seek(MPContext *mpctx, struct seek_params seek)
     if (unlikely(seek.type == MPSEEK_CHAPTER)) {
         mpctx->last_chapter_flag = false;
         seek.type = MPSEEK_ABSOLUTE;
-    } else {
-        mpctx->last_chapter_seek = -2;
     }
 
     bool hr_seek_very_exact = seek.exact == MPSEEK_VERY_EXACT;
@@ -450,6 +448,11 @@ void queue_seek(struct MPContext *mpctx, enum seek_type type, double amount,
     if (mpctx->stop_play == AT_END_OF_FILE)
         mpctx->stop_play = KEEP_PLAYING;
 
+    if (type != MPSEEK_CHAPTER) {
+        mpctx->last_chapter_flag = false;
+        mpctx->last_chapter_seek = -2;
+    }
+
     switch (type) {
     case MPSEEK_RELATIVE:
         seek->flags |= flags;