[TODO] Fix the case that the length of source_datapipe is shorter than limit

[VitalyFedyunin]

This issue is generated from the TODO line

data/torchdata/datapipes/iter/util/header.py

Line 29 in f102d25

# TODO: Fix the case that the length of source_datapipe is shorter than limit

[ejguan]

Assigning to myself as I remember this comment was added by me.