st3m_mode: Call st3m_gfx_flush in st3m_mode_set

This way it also catches things like moving to disk mode, so OSD
gets properly cleared.

components/st3m/st3m_mode.c

@@ -88,11 +88,14 @@ void st3m_mode_set(st3m_mode_kind_t kind, const char *message) {
         _mode.message = NULL;
     }
 
+    if (_mode.kind != kind) {
+        st3m_media_stop();
+        st3m_gfx_flush(200);
+    }
+
     _mode.kind = kind;
     _mode.shown = false;
 
-    st3m_media_stop();
-
     if (kind == st3m_mode_kind_disk_flash) {
         _diskmode_flash();
     }
@@ -142,7 +145,6 @@ void st3m_mode_update_display(bool *restartable) {
         case st3m_mode_kind_repl:
             if (!_mode.shown) {
                 _mode.shown = true;
-                st3m_gfx_flush(200);
                 const char *lines[] = {
                     "Send Ctrl-D over USB",
                     (st3m_io_app_button_is_left())