Chunked-format readers: bound the single-chunk path's sizes too

A block decoder that validates every seek-table entry (payload size <= MAX) often takes a shortcut for a block with one chunk, synthesizing the seek entry from the block footer. That path skips the bound, so a corrupt or hostile footer can make the decoder resize a buffer to the full u32 range (4 GB) before decompression fails. Put the same bound in the footer check (e.g. checkInfo) so open and verify refuse it too. A cheap test: override global operator new in a tiny C++ harness to throw above ~512 MB, and feed the decoder a file whose footer and index claim a huge size while the checksums stay valid.