[Python] Fix robot_wrapper binding

* addMesh returns boolean. Proceed only if addMesh is True

bindings/python/scripts/robot_wrapper.py

@@ -179,7 +179,7 @@ class RobotWrapper(object):
             meshName = self.viewerNodeNames(visual) 
             meshPath = visual.meshPath
             meshScale = visual.meshScale
-            self.viewer.gui.addMesh(meshName, meshPath)
+            if self.viewer.gui.addMesh(meshName, meshPath):
                 self.viewer.gui.setScale(meshName, npToTuple(meshScale))
 
         # Finally, refresh the layout to obtain your first rendering.