Vandle Processor doesn't check for good HRT event before plotting TDIFF

[sztaylor89]

There is not check in VandleProcessor to see if there was a good HRT event before plotting TDIFF. This can lead to a spike in the TDIFF spectrum at TDIFF=0+offset since it plots when no HRT event happened. I would suggest something like what I use in my experiment processor:
if(!bar.GetHasEvent()) {continue;}