add_fiveprimeutr adds UTR that overlaps CDS when UTR is at the start of CDS

[johannesnicolaus]

For some SL peaks, the peak is exactly at the 1st base of the CDS, so that it overlaps the start of CDS. There needs to be a better way to handle this, for example, by extending the transcript by one base upstream.

When sanitizing using AGAT, the UTR is considered supernumerary and gets removed.