Avoid TB_DELETEBUTTON errors when recreating wxMSW wxToolBar

Reset the number of buttons to skip deleting the old buttons in
wxToolBar::Recreate() as these buttons don't exist any more (having been
created in the old control) and trying to delete them just results in
debug error messages from TB_DELETEBUTTON.

src/msw/toolbar.cpp

@@ -519,6 +519,11 @@ void wxToolBar::Recreate()
 
     wxDELETE(m_disabledImgList);
 
+    // Also skip deleting the existing buttons in Realize(): they don't exist
+    // any more, so doing this is unnecessary and just results in errors from
+    // TB_DELETEBUTTON.
+    m_nButtons = 0;
+
     Realize();
 }