"invalid next size" backtrace on use of trim on certain images

• https://metacpan.org/dist/Imager/changes
• https://github.com/tonycoz/imager/issues/534

Imager versions through 1.030 for Perl allow a heap out of bounds (OOB) write on crafted multi-frame GIF files. Imager::File::GIF's i_readgif_multi_low allocates a single per-row buffer GifRow sized for the GIF's global screen width 'SWidth' and reuses it across every image in the file. The page-match branch validates Image.Width + Image.Left > SWidth before each DGifGetLine write, but the parallel skip-image branch at imgif.c:790-805 calls DGifGetLine(GifFile, GifRow, Width) with no such check.

• https://metacpan.org/release/TONYC/Imager-1.031/source/Changes
• https://github.com/tonycoz/imager/commit/782e9c06cc75a0f7eed383f39522f51f44598b04.patch