Regression test for off-by-one palette check error

This adds a file to regression-test the previously introduced off-by-one
error in the check on read for a colormapped PNG with an out-of-range
index (equal or greater than the length of the PLTE).

Previous tests covered all cases except the 8-bit palette case; the
"small" test file contains the "bad" entry at index 254, not 255 so it
passes even if the final byte is not checked.  The new file has the
erroneous entry in the last byte.

Signed-off-by: John Bowler <jbowler@acm.org>
1 file changed