Added handlings for negative end time (#1203)

[ArthLeu]

Formatted with Black this time.

[desh2608]

Alignment times are supposed to be w.r.t. the recording, so I don't see how the start/end could be negative?

See:

lhotse/lhotse/supervision.py

Line 40 in 0089643

class AlignmentItem(NamedTuple):

[pzelasko]

@desh2608 Are we not adjusting alignment times together with supervision times when creating a cut?

@ArthLeu could you add a unit test that would have failed before but will pass correctly now to cover your changes?