Fix incorrect inflateSyncPoint() return value with DFLTCC

Fix incorrect inflateSyncPoint() return value with DFLTCC

DFLTCC does not provide the necessary information to implement
inflateSyncPoint() - Incomplete-Function Status and Incomplete-Function
Length are the fields that provide the relevant information, but
unfortunately it's not enough. If DFLTCC is in use, the current code
checks software decompression state and always returns 0. This
(rightfully) confuses rsync, so fix by returning Z_STREAM_ERROR
instead.