Added missing return.

Rationale:
Slightly more efficient to return right after !IsCompilable()
(with a single message) than relying on falling into the
necessarily true IsMethodUnverified() (with another message).
Note that this subtle change cannot be easily tested (since
behavior is the same), but e.g. 675-checker-unverified-method
at least provides code coverage.

Bug: 72957776
Test: test-art-host
Change-Id: I7044e60e3c10367a1fa024573dc6dbbb5e9243ad