Avoid bogus selection events from keys in generic wxDataViewCtrl

Don't do anything and, in particular, don't send any events if pressing a
navigation key, such as a cursor up/down arrow, didn't actually change the
current item because it was already the first/last one.

This fixes an endless stream of wxEVT_DATAVIEW_SELECTION_CHANGED events if the
up/down arrow is simply kept pressed when the selection is on first/last item.

src/generic/datavgen.cpp

@@ -3806,6 +3806,9 @@ void wxDataViewMainWindow::OnVerticalNavigation(const wxKeyEvent& event, int del
     unsigned int oldCurrent = m_currentRow;
     unsigned int newCurrent = (unsigned int)newRow;
 
+    if ( newCurrent == oldCurrent )
+        return;
+
     // in single selection we just ignore Shift as we can't select several
     // items anyhow
     if ( event.ShiftDown() && !IsSingleSel() )
@@ -3822,14 +3825,12 @@ void wxDataViewMainWindow::OnVerticalNavigation(const wxKeyEvent& event, int del
         }
 
         SelectRows(oldCurrent, newCurrent);
-        if (oldCurrent!=newCurrent)
-        {
+
         wxSelectionStore::IterationState cookie;
         const unsigned firstSel = m_selection.GetFirstSelectedItem(cookie);
         if ( firstSel != wxSelectionStore::NO_SELECTION )
             SendSelectionChangedEvent(GetItemByRow(firstSel));
     }
-    }
     else // !shift
     {
         RefreshRow( oldCurrent );