Handle CgBI chunks consistently when they appear after IHDR by routing both identify/decode paths through a new `ReadCgbiChunk()` method that immediately validates already-read headers. This prevents invalid CgBI images from bypassing compatibility checks when chunk order is unusual. Added PNG tests that reorder the first two chunks to confirm incompatible CgBI headers now throw in both identify and decode flows. Also renames `ZlibInflateStream` to `ZlibInflateReader` and updates EXR/PNG/TIFF call sites for clearer intent.
James Jackson-South