Fix dedicated dict search isSupported() requirements.

[senhuang42]

Currently, asserts in zstd_lazy.c will fail if you try to compress with chainLog > 24 or hLog < cLog with dedicated dict search.

The following command fails on dev:
make -j zstd DEBUGLEVEL=1 && ./zstd [file] -D [dictFile] --zstd=clog=25,hlog=23 -7f

This PR adds the same checks that are assert()ed to be true in zstd_lazy.c when using dedicated dict search, and includes a unit test that fails without this fix.

Though, I will note that dedicated dict search at least seems to work fine when clog > 24 or hLog < cLog, so an alternative could just be to remove the asserts.

[felixhandte]

Cool. Looks good.

As I recall, these asserts are present for the following reasons:

assert(chainLog <= 24);

In the DDSS, the hashtable layout for each entry is:

• 4 bytes: first match index
• 4 bytes: second match index
• 4 bytes: third match index
• 1 byte: number of additional matches in the chain table
• 3 bytes: index of head of chain in chain table

So we only have 24 bits to index into the chain table.

assert(hashLog >= chainLog)

We need this for DDSS table construction, because we first build the chain table in the hash table, and then sort the chains into the chain table proper.