[FIX] Chunk builder's block limit

[noel2004]

When chunk builder deliver chunk data with block limit condition, the original code do not reset the ccc result.

As the result, the following add call would deliver a empty collection of chunks and panic.

This PR fix the issue and add enviroment variant (CHUNK_BLOCK_LIMIT) for setting the block limit of chunk builder.

For not-set, thhe block limit is kept as original code (1) and to enable unlimit of blocks, use CHUNK_BLOCK_LIMIT=0

[lispc]

i guess you find this bug by set block_limit > 1?

[noel2004]

i guess you find this bug by set block_limit > 1?

yes

[0xShankar]

Try Block_limit