lcpit_matchfinder: fix limiting nice_match_len

lcpit_matchfinder: fix limiting nice_match_len

The "normal" mode of the lcp-interval tree matchfinder supports finding
matches up to LCP_MAX bytes.  The "huge" mode, which is needed on
buffers larger than 64 MiB, supports up to HUGE_LCP_MAX bytes.
nice_match_len must be limited to the appropriate one of these values.

But nice_match_len is limited by lcpit_matchfinder_init().  That's
wrong, because it only knows whether huge mode *might* be used later,
based on max_bufsize.  Which mode to use is actually decided on a
buffer-by-buffer basis by lcpit_matchfinder_load_buffer().

Thus, limit nice_match_len in lcpit_matchfinder_load_buffer() instead.

This fixes a crash or incorrect output during LZMS compression with a
compression level > 50 and a chunk size > 64 MiB.