HPCC-9631 - KeyedJoin may miss cached IKeyIndex's

Due to an uninitialized 'crc' variable, that the key index cache
uses to form a key for caching IKeyIndex's. KeyedJoin would
probably have been missing cache hits and consequently, creating
extra IKeyIndex's unecessarily

Signed-off-by: Jake Smith <jake.smith@lexisnexis.com>