removed the ip++ at the beginning of block

removed the ip++ at the beginning of block

The first byte used to be skipped
to avoid a infinite self-comparison.
This is no longer necessary, since init() ensures that index starts at 64K.

The first byte is also useless to search when each block is independent,
but it's no longer the case when blocks are linked.

Removing the first-byte-skip saves
about 10 bytes / MB on files compressed with -BD4 (linked blocks 64Kb),
which feels correct as each MB has 16 blocks of 64KB.