Fix LoadEventNexus when using compression with weighted events and period data

[rosswhitfield]

Description of work

Discovered 2 more bugs in LoadEventNexus when using CompressTolerance similar to #37443

It is due to changes from #37141 which was only added in the 6.10 release.

First it segfaults when using weighted events

ws = LoadEventNexus(Filename="ARCS_sim_event.nxs", CompressTolerance=0.01)

Second it fails when using period data

ws = LoadEventNexus(Filename="LARMOR00003368.nxs", CompressTolerance=0.01)

fails with

RuntimeError: EventList::getWeightedEvents() called for an EventList not of type WeightedEventNoTime. Use getEvents() or getWeightedEvents().

Summary of work

Fixes There is no associated issue.

Further detail of work

To test:

Check that the above no longer fail

This does not require release notes because this bug was only introduced during this release.

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[jmborr]

code looks good and manual tests pass