Prevent race condition in entity filtering

[jansupol]

Signed-off-by: Jan Supol [email protected]

[jansupol]

Unfortunately, I was not able to come up with a solid reproducer/test.

However, when one thread stored a graph graphProvider.getOrCreateEntityGraph(entityClass, forWriter), another thread used the graph before the graph was populated by the first thread. It resulted in a situation where everything was filtered out in an HTTP response, as the unpopulated graph did not contain the entities that should not have been filtered out.

[jansupol]

Fixes #4189 #4187

[tomas-langer]

LGTM as long as there are no side effects to creating a new instance of the EntityGraph