Fix keyboard navigation crash in single column generic wxDataViewCtrl

Selecting a leaf node in a wxDataViewCtrl and then pressing the right arrow
key resulted in using an out-of-bounds index for accessing the columns list.

Fix this by setting the current column to the first one, and not to the second
one which might not exist.

See #17537.

(cherry picked from commit 5d671d8136)

src/generic/datavgen.cpp

@@ -4006,7 +4006,7 @@ bool wxDataViewMainWindow::TryAdvanceCurrentColumn(wxDataViewTreeNode *node, boo
     {
         if ( forward )
         {
-            m_currentCol = GetOwner()->GetColumnAt(1);
+            m_currentCol = GetOwner()->GetColumnAt(0);
             m_currentColSetByKeyboard = true;
             RefreshRow(m_currentRow);
             return true;