Correct wxWindowQt::DoSetSize() for possible NULL member de-reference.

Thanks David Register

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@78376 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/qt/window.cpp

@@ -856,7 +856,7 @@ void wxWindowQt::DoSetSize(int x, int y, int width, int height, int sizeFlags )
     // if a control is created with size of zero, it is set as hidden by qt
     // if it is then resized, in some cases it remains hidden, so it
     // needs to be shown here
-    if (!m_qtWindow->isVisible() && IsShown())
+    if (m_qtWindow && !m_qtWindow->isVisible() && IsShown())
         m_qtWindow->show();
 }