Out-of-bounds read in Imager

Summary

Imager versions from 0.45_02 before 1.035 for Perl read outside the EXIF block via unchecked start offsets in tiff_load_ifd. tiff_load_ifd() validates an IFD entry's data by checking that `entry->offset + entry->size` stays within the EXIF block, and never checks the start offset itself. Where that sum is not the real end of the data, the check passes with the entry starting outside the block. Through 1.032 `entry->offset` is a plain int, so on the usual two's-complement implementations an offset with the high bit set converts to negative and the sum can land back inside the block. From 1.033 the field is a size_t and the addition wraps only where size_t is 32 bits. The IFD's own start offset is checked the same way and wraps where unsigned long is 32 bits, which includes 64-bit Windows. Any caller of Imager->read() on an attacker-supplied image may receive EXIF tags holding bytes from outside the block, or crash the process.