MacOS: Catch all exceptions thrown by wxCFEventLoop::OSXDoRun() for cocoa modal dialog.

The cocoa framework is not bug-free.
Some version(I'd called it buggy) may throw unexpected exceptions.
In order to avoid the ShowModal() to died and break the modal stack, and finally comes you
a assertion failure on broken modal stack, we should catch exceptions here.

Author: 徐扬斌

src/osx/cocoa/evtloop.mm

@@ -434,7 +434,15 @@ static NSUInteger CalculateNSEventMaskFromEventCategory(wxEventCategory cat)
     if ( m_modalWindow )
     {
         BeginModalSession(m_modalWindow);
-        wxCFEventLoop::OSXDoRun();
+		while(true){
+			try {
+				wxCFEventLoop::OSXDoRun();
+				break;
+			}
+			catch(...){
+				printf("wxModalEventLoop::OSXDoRun caught unknown exception\n");
+			}
+		}
         EndModalSession();
     }
     else