player: make stop command actually stop

The stop command didn't always stop. In this case, opening a HLS URL and
then sending "stop" during loading would actually make it fallback to
parsing it as a playlist, and then continued to play the playlist items.
(This corner case makes several unfortunate factors come together to
produce this really odd behavior.)

Another issue is that the "stop" was not always explicitly set. This
could be a problem when sending several commands at once. Only the
"quit" command should have priority over the "stop" command, so this is
still checked.

player/command.c

@@ -4588,7 +4588,7 @@ int run_command(struct MPContext *mpctx, struct mp_cmd *cmd, struct mpv_node *re
 
     case MP_CMD_STOP:
         playlist_clear(mpctx->playlist);
-        if (!mpctx->stop_play)
+        if (mpctx->stop_play != PT_QUIT)
             mpctx->stop_play = PT_STOP;
         break;
 

player/loadfile.c

@@ -1097,7 +1097,7 @@ reopen_file:
     }
 
     open_demux_reentrant(mpctx);
-    if (!mpctx->master_demuxer)
+    if (!mpctx->master_demuxer || mpctx->stop_play)
         goto terminate_playback;
     mpctx->demuxer = mpctx->master_demuxer;