Fix for sheets based on NSAlert.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@59351 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/osx/cocoa/utils.mm

@@ -173,7 +173,9 @@ void wxMacWakeUp()
 {
     resultCode = returnCode;
     sheetFinished = YES;
-    [sheet orderOut: self];
+    // NSAlerts don't need nor respond to orderOut
+    if ([sheet respondsToSelector:@selector(orderOut:)])
+        [sheet orderOut: self];
 }
 @end