Fix instrumentation stack tracking

We were incorrectly tracking the instrumentation stack, bailing out of
installation early. This could lead to missing instrumentation events,
failing CHECKs or (potentially) corrupt thread stacks.

Test: ./test.py --host --trace --ntrace --stream -j50
Test: Use gapid.

Bug: 67384421
Bug: 74386428

Change-Id: I91686ac4f44550d89b9d7a5f716df88f505d91b1