player: restore old/correct --force-window behavior

When playback of a video ends, and the next file has no video at all (no
cover art or anything), then the window must be cleared.

This also resizes the window forcibly, which is by design.

Fixes #2825.

player/loadfile.c

@@ -1321,6 +1321,9 @@ reopen_file:
             "Displaying attached picture. Use --no-audio-display to prevent this.\n");
     }
 
+    if (!mpctx->vo_chain)
+        handle_force_window(mpctx, true);
+
     MP_VERBOSE(mpctx, "Starting playback...\n");
 
     mpctx->playback_initialized = true;