IPTC metadata: Fix an off-by-one error.
IPTC metadata: Fix an off-by-one error.

Fixes an issue where a single-byte value at the end of an IPTC directory
would not be sufficient to consider the number of remaining bytes
sufficient, causing the extraction to be halted prematurely.

Nadahar/metadata-extractor,Nadahar/metadata-extractor,PaytonGarland/metadata-extractor,rcketscientist/metadata-extractor,Widen/metadata-extractor,drewnoakes/metadata-extractor