[CodeGen][MISched] Handle empty sized resource usage. (#75951)

TargetSchedule.td explicitly allows the usage of a ProcResource for zero
cycles, in order to represent that the ProcResource must be available
but is not consumed by the instruction. On the other hand,
ResourceSegments explicitly does not allow for a zero sized interval. In
order to remedy this, this patch handles the special case of when there
is an empty interval usage of a resource by not adding an empty
interval.

We ran into this issue downstream, but it makes sense to have
this upstream since it is explicitly allowed by TargetSchedule.td.