bounding volume results are not checked for validity in concurrent calcuation

There is one important difference between the single threaded and the concurrent flow of calculating the bounding volumes: the linear one checks for validity of the results, the concurrent one doesn't. This leads to crashes in my application, as non valid bounding boxes are added to be processed later, which then access the entity-pointer set to nullptr.

The single threaded path is in src/core/jobs/calcboundingvolumejob.cpp, line 288, the concurrent on line 143.