fix a few more fuzzes

Minor changes to fix some fuzz conditions.
A couple of ignored asserts when the data
is fuzzy, and one fail condition when the
underlying data has already been deleted.

TBR=reed@google.com
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2443243002

Review-Url: https://codereview.chromium.org/2443243002
3 files changed