Chromium's test suite contains an RLE image that reports a certain
file size in the header, but then contains additional encoded data.
Our bmp decoder would only decode half of the image, before stopping.
With this fix, we check for additional data before returning
kIncompleteInput.
If this lands, I will upload the test image to the bots.
Also adding an invalid image test to CodexTest.
BUG=skia:
Review URL: https://codereview.chromium.org/1273853004
