Make kInvalidConversion a fatal failure in DMSrcSink

We just need to abort early on tests that we know
are invalid conversions.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1704433003

Review URL: https://codereview.chromium.org/1704433003
2 files changed