Check for uninitialized memory during jpeg encode

Bug: chromium:951893

This will help determine which piece of code left memory uninitialized.
Add a test that exercises all the different ways we might pass memory
to jpeg_write_scanlines.

Change-Id: I6392a414795da9b0471e8cd6b373a7fff8f0a1b1
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/225098
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Leon Scroggins <scroggo@google.com>
2 files changed