Make ICO fail on truncated data

If all the data has been received, but decoding is not complete, mark
the ICOImageDecoder as having failed. This was already the case for
BMP in ICO; make PNG in ICO match. Add a test.

Brought up in crrev.com/2754003008

Review-Url: https://codereview.chromium.org/2761303003
Cr-Commit-Position: refs/heads/master@{#458731}
2 files changed