don't use annoying and unneeded in C++ casts of NULL to "T *" in all other files neither

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@58227 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/appcmn.cpp

@@ -71,7 +71,7 @@ WXDLLIMPEXP_DATA_CORE(wxList) wxPendingDelete;
 
 wxAppBase::wxAppBase()
 {
-    m_topWindow = (wxWindow *)NULL;
+    m_topWindow = NULL;
 
     m_useBestVisual = false;
     m_forceTrueColour = false;