Add protection for very low energy events

Jon Burrrequested to merge
jburr/athena:FixATR-26351 into 22.0

Fixes ATR-26351.

This introduces a fix to the TCPufitFex that was already applied to the PUSplitPufitFex algorithm. When there are only a very small number of towers with any energy in the event then the fit to pileup fails and it should just be skipped.

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