XLALCalculatePulsarCrossCorrStatistic(): added explicit memory-bound check

  - this causes testPulsarCrossCorr_v2.sh to fail now, triggering a
    bug that was previously resulting in a memory-violation error only
    on Mac-OSX, apparently
  - refs #1168
PulsarCrossCorr_v2: refined Reinhard's error checking

  -- Check loops over both indices
  -- Now check just once before each loop
  -- refs #1168