player: add --force-window=immediate mode

This creates the window before the first file is loaded. This was
requested a bunch of times, but on the other hand a change to make this
behavior the default was reverted some time ago, because other users
hated it.

player/main.c

@@ -472,6 +472,8 @@ int mp_initialize(struct MPContext *mpctx, char **options)
                     "the selected video_out (-vo) device.\n");
             return -1;
         }
+        if (opts->force_vo == 2)
+            handle_force_window(mpctx, false);
         mpctx->mouse_cursor_visible = true;
     }