ART: Properly check for attached thread in CheckJNI

The previous implementation checked too late, as the required
ScopedObjectAccess would have already aborted. Instead, preface
all necessary functions with an explicit check.

Performance should be almost neutral, as the test is only moved
earlier, but not duplicated.

(cherry picked from commit fb8f75c1)

Bug: 78135453
Test: m test-art-host-gtest-jni_internal_test
Merged-In: I7b98744e9a3895e84ba9e2661975ce29722076c3
Change-Id: I7b98744e9a3895e84ba9e2661975ce29722076c3