update fullscreen state when it is changed by the WM

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@72921 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/gtk/toplevel.cpp

@@ -382,6 +382,9 @@ gtk_frame_window_state_callback( GtkWidget* WXUNUSED(widget),
         win->HandleWindowEvent(evt);
     }
 
+    if (event->changed_mask & GDK_WINDOW_STATE_FULLSCREEN)
+        win->m_fsIsShowing = (event->new_window_state & GDK_WINDOW_STATE_FULLSCREEN) != 0;
+
     return false;
 }
 }