Fix a memory leak when decoding corrupted indexed PNGs.
Commit to branch refs/heads/png-leak

BUG=skia:3457

Committed: https://skia.googlesource.com/skia/+/561a1ca9559a1ea7589ab93350124284fcef3315

Review URL: https://codereview.chromium.org/951663002
3 files changed