rm warning rotation types

Former-commit-id: aeb8afa12937f432cf05e1dd82010f83955ac387

include/igl/viewer/Viewer.cpp

@@ -544,6 +544,8 @@ namespace viewer
         {
           switch(core.rotation_type)
           {
+            default:
+              assert(false && "Unknown rotation type");
             case ViewerCore::ROTATION_TYPE_TRACKBALL:
               igl::trackball(core.viewport(2),
                              core.viewport(3),