Fix crash when auto-sizing a wxDataViewCtrl column.

The code was confused about the difference between the model and view columns
indices and incorrectly used the former as the latter, which could result in
an out of bound array access.

Closes #15420.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74889 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/generic/dataview.h

@@ -227,6 +227,9 @@ public:     // utility functions not part of the API
     // return the index of the given column in m_cols
     int GetColumnIndex(const wxDataViewColumn *column) const;
 
+    // Return the index of the column having the given model index.
+    int GetModelColumnIndex(unsigned int model_column) const;
+
     // return the column displayed at the given position in the control
     wxDataViewColumn *GetColumnAt(unsigned int pos) const;