Ensure that an event loop exists in ShowViewOrWindowWithEffect().

We may not have an event loop yet if wxWindow::ShowWithEffect() is called
during the application startup, create a temporary event loop instead of
crashing in this case.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@62309 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/osx/cocoa/window.mm

@@ -1395,9 +1395,12 @@ wxWidgetCocoaImpl::ShowViewOrWindowWithEffect(wxWindow *win,
     //
     // notice that because the default animation mode is NSAnimationBlocking,
     // no user input events ought to be processed from here
+    {
+        wxEventLoopGuarantor ensureEventLoopExistence;
         wxEventLoopBase * const loop = wxEventLoopBase::GetActive();
         while ( ![animDelegate isDone] )
             loop->Dispatch();
+    }
 
     if ( !show )
     {