FIX #259 Regress change variable change from int to unsigned
FIX #259 Regress change variable change from int to unsigned

A previous change from int to unsigned meant that an array index x-2
became a very high number when it underflowed.

Signed-off-by: Gavin Halliday <2edfa8aca9fb78974188e5b35be8b52d4e4967ae@lexisnexis.com>

RussWhitehead/HPCC-Platform,RussWhitehead/HPCC-Platform,RussWhitehead/HPCC-Platform,afishbeck/HPCC-Platform,RussWhitehead/HPCC-Platform,RussWhitehead/HPCC-Platform,afishbeck/HPCC-Platform,afishbeck/HPCC-Platform,afishbeck/HPCC-Platform,afishbeck/HPCC-Platform,afishbeck/HPCC-Platform,RussWhitehead/HPCC-Platform,RussWhitehead/HPCC-Platform