RAR5 reader: handle a case with truncated huffman tables.

RAR5 reader: handle a case with truncated huffman tables.

RAR5 reader did assume that the block contains full huffman table data.
In invalid files that declare existence of huffman tables, but also
declare too small block size to fit the huffman tables in, RAR5 reader
was interpreting memory beyond the allocated block.

The commit adds necessary buffer overflow checks and fails the huffman
table reading function in case truncated data will be detected.

The commit also provides a unit test for this case.

Should fix OSSFuzz issue #12817.