Guard against unknown/invalid pixel id's in the 'Precount' functionality of LoadEventNexus

[Russell Taylor]

It's been discovered that if a file contains events assigned (event_id field in the nexus file) to an unknown pixel ID (i.e. one not in the IDF) then there's potential for a bad_alloc when the 'Precount' option tries to allocate the vectors. The code doesn't protect against this happening so can end up getting the calculation wrong and trying to allocate very large vectors. We need to catch this - as presumably the code that actually loads the events does.

[Russell Taylor]

Re #8542. Protect against unknown pixel id's.

Specifically, when all the IDs in a bank are higher than the highest known one from the instrument definition.

Changeset: 0650416cca9ebe7e915102f1283c6db690db3fa1

[Russell Taylor]

Re #8542. Co-locate related code.

Just moved up a piece of code - nothing functional has changed.

Changeset: 5d1e79c1a09b4a9229b321b16511c8e885e99bd6

[Russell Taylor]

This addresses the problem seen here, which relates to pixel ID's that are larger than the highest number in the IDF (#7524 handled the case of unknown pixel IDs within the range given by the IDF).

To test (will need to be at SNS to get the data):

• Load SEQ_43974.nxs.h5 into Mantid. Make sure the 'Precount' option is set to on.
• Before the changes, the algorithm fails with a 'bad_alloc'. After the changes, all is sweet.

[Michael Reuter]

Merge remote-tracking branch 'origin/bugfix/8542_loadeventnexus_bad_alloc'

Full changeset: ​abf16dea737612aafbc8c0eb88eab5f30b2483fb

[Stuart Campbell]

This ticket has been transferred to github issue ​9386