Summary: RCTDevSettings incorrectly assigned "bad" executor-override class to the executor instead of checking if the class exists before assigning it. It should really check if the class exists, and fallback to defaults otherwise.
Reviewed By: mmmulani, yungsters
Differential Revision: D4655926
fbshipit-source-id: 48c8fe28f22aaa8430752411ce5e6e858dbd4b32