Fix bug in STS reco with incorrect indices of digis in time-based reconstruction mode.
There was a bug in event-based local STS reconstruction concerning the indices of the digis in the input array. The bug was reported by N. Herrmann and S. Roy by email; N. Herrmann proposed the proper fix. The bug appeared in event-based reconstruction (digi event builder) after time-based simulation (or for real data from mCBM) in the new CbmRecoSts class, which was introduced in the standard macros on 10 April 2020. It is thus present in the APR20 release.