detectImageFormat read the VP8X (extended WebP) canvas width/height with a
big-endian readBE24, but the WebP spec stores them as 24-bit LITTLE-endian
(Minus-One). A 1920×1080 image was reported as 8324865×3605505, so the
fileInfo sent to highway was garbage and QQ cropped the thumbnail. VP8
(readLE16) and VP8L (readLE32) were already correct.
- Replace readBE24 with readLE24 in the VP8X branch; readBE24 had no other
caller, so it's deleted (no dead code left).
- Add the previously-absent detectImageFormat regression suite (12 cases):
PNG/GIF/BMP/VP8/VP8L/VP8X/JPEG + JPEG DHT-skip + truncated/unknown
fallbacks. The VP8X cases pin little-endian byte order, including the
exact bytes from the issue and an asymmetric 256×1 case that a BE misread
would blow up to 16711681.
Verified TDD red→green: the 3 VP8X cases failed before the one-helper swap,
all 12 pass after.
DrSmoothl