Support non-standard Ifd layout
The output from one popular program on the mac, GraphicConverter, seems to
created exif headers unreadable by exiv2. The interesting part is that other
programs, like Photoshop and iVew, can still successfully read the header.
The error message is:
"Offset of the 1st data entry of IFD0 is out of bounds:
Offset = 4294960962, exceeds buffer size by 4294960458 Bytes"
(Reported by Jeffrey J. Early)
The layout of IFD0 does not conform to that described in the Exif standard: The section containing tag data which occupies >4 bytes is before the IFD directory structure. However there is nothing technically wrong with the IFD, the problem is that class Exiv2::Ifd cannot handle negative offsets (relative to the start of the IFD).