Bugfix for test_FluxesReader unit test
Bugfix for test_FluxesReader unit test

Correcting an array overflow flagged up when building with clang++, which caused the test to exit ungracefully.
iakovos-panourgias/fluidity,jjo31/ATHAM-Fluidity,iakovos-panourgias/fluidity,jjo31/ATHAM-Fluidity,jrper/fluidity,jrper/fluidity,jjo31/ATHAM-Fluidity,jrper/fluidity,jrper/fluidity,iakovos-panourgias/fluidity,jrper/fluidity,iakovos-panourgias/fluidity,jjo31/ATHAM-Fluidity,iakovos-panourgias/fluidity,jjo31/ATHAM-Fluidity