Fix autocorrelation matrix and sigmasq loading from xml when non sequential IFOs are chosen.

At the moment, if non sequential IFOs are chosen such as HV or LK, the autocorrelation matrix and sigmasq array are improperly loaded and do not contain data for the subsequent IFO. This MR should fix that.

The issue for this MR is #81 (closed).

The output of the test for this MR is held at /fred/oz996/ldavis/artifacts/HLVK-1187006000-300/ldavis__fix_xml_parsing-e2737adfc/
A test with bank files input in reverse order is held at /fred/oz996/ldavis/artifacts/HLVK-1187006000-300/ldavis__fix_xml_parsing-e2737adfc-reverse-banks/
A HL zerolag comparison of this MR and the last spiir-O4 commit is held here /fred/oz996/ldavis/artifacts/HLVK-1187006000-300/bc0bee622-vs-e2737adfc.txt there are no differences.