Fix Ogre::ItemIdentityException when loading mesh (#1105)
Fix Ogre::ItemIdentityException when loading mesh (#1105)

When loading a mesh without a material defined rviz crashes with error:
terminate called after throwing an instance of 'Ogre::ItemIdentityException'
  what():  ItemIdentityException: Resource with the name RVIZ/ShadedRed0Robot already exists.
ros-visualization/rviz,ros-visualization/rviz,ros-visualization/rviz,ros-visualization/rviz,ros-visualization/rviz