Q3DScatter should fail gracefully when mesh is missing UV coordinates

The Q3DScatter chart crashes when .obj file is is missing UV coordinates. The sample crashes with shuttle.obj and teapot.obj. Instead of crashing, the Qt should be able to fail gracefully in this case.

To reproduce, please run the attached example project and the application should crash.

If you open the file "scatter.cpp" and locate the line setting the mesh using "setMeshFile" and use OBJ_PLANE or OBJ_CUBE instead, the application does not crash.