Check GetValueFromEditorCtrl() return code in wxDataViewCtrl code.

Don't do anything when finishing editing an item if its new value couldn't be
retrieved.

See #16912.

src/common/datavcmn.cpp

@@ -746,7 +746,8 @@ bool wxDataViewRendererBase::FinishEditing()
         return true;
 
     wxVariant value;
-    GetValueFromEditorCtrl( m_editorCtrl, value );
+    if ( !GetValueFromEditorCtrl(m_editorCtrl, value) )
+        return false;
 
     wxDataViewCtrl* dv_ctrl = GetOwner()->GetOwner();