Exit loop earlier for bsdiff's pathological case

Looking at bsdiff's comment, original author want to generate a diff
patch only if diff is no smaller than 8 bytes. Actual code only only
permits the diff to be generated if diff > 8 bytes.

Partners reported a pair of problematic files where BSDIFF takes more
than 10 hours(input file is only ~80MB). After applying this patch,
bsdiff takes ~1 minute.

To make sure this patch does not harm patch size for non-pathological
cases, I tested multiple pixel OTAs. Total OTA size increased by just
0.002% . Basically negligible.

Test: Multiple pixle OTAs
Bug: 285271992

Change-Id: I2a9b52939f8d17ea48dc2908942b2cc21cbe4e09
2 files changed