Mac OS: Added necessary check because a non-FLTK window can be found

as child of an FLTK window when turning a window full-screen.

git-svn-id: file:///fltk/svn/fltk/branches/branch-1.3@10909 ea41ed52-d2ee-0310-a9c1-e6b18d33e121

src/Fl_cocoa.mm

@@ -715,7 +715,7 @@ - (void)recursivelySendToSubwindows:(SEL)sel
   NSEnumerator *enumerator = [[self childWindows] objectEnumerator];
   id child;
   while ((child = [enumerator nextObject]) != nil) {
-    [child recursivelySendToSubwindows:sel];
+    if ([child isKindOfClass:[FLWindow class]]) [child recursivelySendToSubwindows:sel];
   }
 }