Previously, in the case of RLE4, parsing took suspiciously long.
What happened was that 'pixel_count' was 255, and 'i' was incremented
by *two* in each iteration, so the for-loop continued until the
entire output buffer was full, and then rejected the RLE data
as bogus.
This little diff allows pixel_count to reach 256, be greater than
pixel_count, and thus terminate the loop in the intended way.
aec8983819