Fix the return value of wxSimpleHtmlListBox::Insert().

The returned index was off by 1.

Closes #12717.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@66277 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/generic/htmllbox.cpp

@@ -686,7 +686,7 @@ int wxSimpleHtmlListBox::DoInsertItems(const wxArrayStringsAdapter& items,
 
     UpdateCount();
 
-    return pos;
+    return pos - 1;
 }
 
 void wxSimpleHtmlListBox::SetString(unsigned int n, const wxString& s)