FileChooser: Ensure preview mouse interactions work when showing dialog on macOS

modules/juce_gui_basics/native/juce_mac_FileChooser.mm

@@ -171,6 +171,9 @@ public:
 
             enterModalState (true);
             [panel beginWithCompletionHandler:CreateObjCBlock (this, &Native::finished)];
+
+            if (preview != nullptr)
+                preview->toFront (true);
         }
     }