initialize the variable as XtVaGetValues() may not do it apparently [backport from HEAD]

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_2_8_BRANCH@46386 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/motif/window.cpp

@@ -641,7 +641,7 @@ void wxWindow::SetLabel(const wxString& label)
 
 wxString wxWindow::GetLabel() const
 {
-    char *label;
+    char *label = NULL;
     XtVaGetValues((Widget)GetMainWidget(), XmNtitle, &label, NULL);
 
     return wxString(label);