ART: Correct static invariant checks

Instances of initializing classes may leak to other threads. It is
legal to execute methods and access fields, as long as they are not
static. However, the class should still be initializing (or already
be erroneous). Replace checks with this weaker invariant.

Follow-up to commit 4e99b3d8.

Bug: 15899971
Bug: 62478025
Bug: 67719550
Test: m test-art-host
Change-Id: I63190253759df95ca54e40fd4117a24e12e0c069