Add a checker for signature boundary in verifier

The 'signature_start' variable marks the location of the signature
from the end of a zip archive. And a boundary check is missing where
'signature_start' should be within the EOCD comment field. This causes
problems when sideloading a malicious package. Also add a corresponding

Bug: 31914369
Test: Verification fails correctly when sideloading on

Change-Id: I6ea96bf04dac5d8d4d6719e678d504f957b4d5c1
(cherry-picked from f69e6a9475983b2ad46729e44ab58d2b22cd74d0)
(cherry picked from commit 54ea136fded56810bf475885eb4bd7bf1b11f09c)
1 file changed