jxl-frame: TOC entry count limit

[EugeneVert]

Prevent OOM on invalid images with enormous amount of toc_entries

https://github.com/libjxl/libjxl/blob/c2e546a17fa579748edae2667ebb04e1a9a61783/lib/jxl/toc.cc#L25-L30

[tirr-c]

Level 10 specifies width * height <= (1 << 40), we can have at most 11 passes from 4 + u(3), and minimum group_dim is 128 (1 << 7), so in an extreme case we have:

• 1 LfGlobal,
• (1 << 40) / ((1 << 7) * 8 * (1 << 7) * 8) = 1_048_576 LfGroups,
• 1 HfGlobal,
• (1 << 40) / (1 << 14) * 11 = 738_197_504 PassGroups

...and this yields 739 246 082 TOC entries. Well, this feels too large. Maybe I'll just go with 65536.