SkWuffsCodec: Initialize memory when incomplete

Bug: oss-fuzz:11800

We already had code that initialized the output memory, but it assumed
that we would later copy from wuffs' work buffer. If the dirty rect is
empty, we don't do that. Rearrange the wuffs decode so we can know that
the dirty rect is empty when we decide whether to initialize.

Change-Id: I45fdd4270906b4c240ec087d20c24fb107a1dc07
Reviewed-on: https://skia-review.googlesource.com/c/189866
Commit-Queue: Leon Scroggins <scroggo@google.com>
Reviewed-by: Nigel Tao <nigeltao@google.com>
1 file changed