[Mac] Fix ref count bug when disposing popups

Xwt.XamMac/Xwt.Mac/PopupWindowBackend.cs

@@ -546,17 +546,20 @@ protected override void Dispose(bool disposing)
 				{
 					if (VisibilityEventsEnabled() && ContentView != null)
 						ContentView.RemoveObserver(this, HiddenProperty);
-
-					// HACK: Xamarin.Mac/MonoMac limitation: no direct way to release a window manually
-					// A NSWindow instance will be removed from NSApplication.SharedApplication.Windows
-					// only if it is being closed with ReleasedWhenClosed set to true but not on Dispose
-					// and there is no managed way to tell Cocoa to release the window manually (and to
-					// remove it from the active window list).
-					// see also: https://bugzilla.xamarin.com/show_bug.cgi?id=45298
-					// WORKAROUND:
-					// bump native reference count by calling DangerousRetain()
-					// base.Dispose will now unref the window correctly without crashing
-					DangerousRetain();
+
+					if (WindowBackend.XamMacDangerousDispose)
+					{
+						// HACK: Xamarin.Mac/MonoMac limitation: no direct way to release a window manually
+						// A NSWindow instance will be removed from NSApplication.SharedApplication.Windows
+						// only if it is being closed with ReleasedWhenClosed set to true but not on Dispose
+						// and there is no managed way to tell Cocoa to release the window manually (and to
+						// remove it from the active window list).
+						// see also: https://bugzilla.xamarin.com/show_bug.cgi?id=45298
+						// WORKAROUND:
+						// bump native reference count by calling DangerousRetain()
+						// base.Dispose will now unref the window correctly without crashing
+						DangerousRetain();
+					}
 					// tell Cocoa to release the window on Close
 					ReleasedWhenClosed = true;
 					// Close the window (Cocoa will do its job even if the window is already closed)

Xwt.XamMac/Xwt.Mac/WindowBackend.cs

@@ -475,7 +475,7 @@ public void SetMainMenu (IMenuBackend menu)
 
 		static Selector closeSel = new Selector ("close");
 
-		static readonly bool XamMacDangerousDispose = Version.Parse(Constants.Version) < new Version(5, 6);
+		internal static readonly bool XamMacDangerousDispose = Version.Parse(Constants.Version) < new Version(5, 6);
 
 		bool disposing, disposed;