player: reset playback abort when reloading a file

PT_RELOAD_FILE is a somewhat obscure case when using DVB or when
switching Matroska editions. Both cases were broken, because the
asynchronous playback abort mechanism was still triggered. This
mechanism is used to force the demuxer and stream layers to exit
immediately (instead of blocking on I/O possibly forever), and
is normally disabled on playback start. The reopen path is a bit
strange, and needs to reset it manually.

Pointed out in #2568.

player/loadfile.c

@@ -1265,6 +1265,7 @@ static void play_current_file(struct MPContext *mpctx)
 
     if (mpctx->stop_play == PT_RELOAD_FILE) {
         mpctx->stop_play = KEEP_PLAYING;
+        mp_cancel_reset(mpctx->playback_abort);
         goto reopen_file;
     }