Adding a check on particle level cluster size

Hi,

I just realize that in very rare events the cut on charged constituent of a jet remove all the constituents of the particle level jets, so the code crash if a protection is not added (only in the particle flow case) Since this happen just in few random events I realized this running on the GRID and it didn't come out in local tests.

I simply added the protection.

Cheers Federica

This MR fixes a bug introduced in !21104 (merged). See also ANALYSISTO-761.