Don't try to report non-existent stats

During OTAPreopt we don't have compilation stats due to the way we
compile things. Don't attempt to report stats in this case since it
will cause an NPE.

Test: manual OTA on a blueline
Bug: 181182967
Bug: 177694884
Change-Id: Ie2eb4d7e2ab562d4436a605bcbdd2ea17517dfc3