Passing dummy invalid hits to CMSSW

[areinsvo]

Opening an issue so we don't forget: CMSSW expects a dummy invalid hit as a placeholder for missing hits. Right now we do not add a dummy hit, which means material effects might not be applied correctly and could cause a small pt bias in the final fit.

See relevant comments in the code: https://github.com/trackreco/cmssw/blob/CMSSW_11_2_0_mkFit_X/RecoTracker/MkFit/plugins/MkFitOutputConverter.cc#L200-L214