Fix for #15715: NULL check required in wxRichTextBuffer::SetStyleSheetAndNotify()

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@75312 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/richtext/richtextbuffer.cpp

@@ -8726,7 +8726,10 @@ bool wxRichTextBuffer::SetStyleSheetAndNotify(wxRichTextStyleSheet* sheet)
 
     wxRichTextEvent event(wxEVT_RICHTEXT_STYLESHEET_REPLACING, winid);
     event.SetEventObject(GetRichTextCtrl());
+    if (GetRichTextCtrl())
         event.SetContainer(GetRichTextCtrl()->GetFocusObject());
+    else
+        event.SetContainer(this);
     event.SetOldStyleSheet(oldSheet);
     event.SetNewStyleSheet(sheet);
     event.Allow();