Fix the stack decoder.

Trying to decode a stack with a dex pc frame which comes from an
apk, the script throws a number of errors. Fix those errors.

Bug: 356896129

Test: Ran a backtrace with an apk and verified it properly shows the right
Test: file and doesn't emit any crashes.
Change-Id: I883e72e71d97b44c57d82664e6198d40164478a0
2 files changed