Don't update checksum if data ptr is null.

Passing a nullptr to adler32 resets it to its initial value.

Bug: 28874264

(cherry-picked from commit 2c6b49498e2f084ce217fcd3327103eadc1e0c37)

Change-Id: I9ac1b66004d4028a67aca18057c03ba9fb494041
2 files changed