Fix bug in GetRowByItem() in generic wxDataViewCtrl

If the item was not found at all, which can happen if all its parents
are not expanded, this function still returned a valid but completely
wrong row index.

This affected many functions which could call it for the items which
were not necessarily visible, i.e. all of them except for the event
handlers as events can only affect the visible items, including but not
limited to SetCurrentItem(), all the selection-related functions, all
the expansion-related functions, EnsureVisible(), HitTest() and
GetItemRect().

src/generic/datavgen.cpp

@@ -3920,7 +3920,9 @@ int wxDataViewMainWindow::GetRowByItem(const wxDataViewItem & item) const
         // the parent chain was created by adding the deepest parent first.
         // so if we want to start at the root node, we have to iterate backwards through the vector
         ItemToRowJob job( item, parentChain.rbegin() );
-        Walker( m_root, job );
+        if ( !Walker( m_root, job ) )
+            return -1;
+
         return job.GetResult();
     }
 }