PFEGamma bug fix : merging loop was terminating early

Discovered in the process of refactoring PFBlockAlgo.

The bug was causing the number of merged EG candidates to change as a function of the order of elements in the PFBlock. Simply put, the testin for continuing to check for a merge was incorrect, and only ever looked at the first element. This effect was somewhat reduced since a relatively 'nice' ordering ordering of objects was guaranteed in the old version of PFBlockAlgo.

There is a ~2% effect on the background only in wf25202.