Check that wxFindReplaceDialog parent is non-null before using it

Although this dialog is normally supposed to have a valid parent, don't
crash if it doesn't have one when any of its buttons are pressed.

src/common/fddlgcmn.cpp

@@ -90,7 +90,8 @@ void wxFindReplaceDialogBase::Send(wxFindDialogEvent& event)
         // because the dialog is a top level window, so do it manually as
         // in 9 cases out of 10 the message must be processed by the dialog
         // owner and not the dialog itself
-        (void)GetParent()->ProcessWindowEvent(event);
+        if ( GetParent() )
+            (void)GetParent()->ProcessWindowEvent(event);
     }
 }