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/gtk1/bmpbuttn.cpp

@@ -206,7 +206,7 @@ void wxBitmapButton::OnSetBitmap()
     if (!the_one.Ok()) the_one = m_bmpNormal;
     if (!the_one.Ok()) return;
 
-    GdkBitmap *mask = (GdkBitmap *) NULL;
+    GdkBitmap *mask = NULL;
     if (the_one.GetMask()) mask = the_one.GetMask()->GetBitmap();
 
     GtkWidget *child = BUTTON_CHILD(m_widget);