HTCC stops building clusters if a clusters that fails selection cuts is found

Created by: raffaelladevita

The cluster finding method returns null if a cluster is found but doesn't satisfy the selection cuts. This stops the while loop at https://github.com/JeffersonLab/coatjava/blob/5bd1800f339f8d2b7d8b1947f2c3eb6902beb71b/reconstruction/htcc/src/main/java/org/jlab/rec/htcc/HTCCReconstruction.java#L65 preventing other good clusters to be found.