compress: better handle `dictBuilder overflow` case

[AskAlexSharov]

If we producing many good pattren-candidates: they will come to dict-builder.
And dict-builder will sort them first by score then alphabetically (and evict tail).
it means high chance to see in dictBuilder 00 and 001 words (begin of alphabet) and don't see ff (end of alphabet).

Need: or better filter candidates before dictBuilder, or improve dictBuilder sorting logic, or do any other tricks. Or add one more limit: "soft limit of dict builder", "hard limit of dict builder", "hard limit of final dictionary".

[VBulikov]

VBulikov added Imp2 as Importance