Handle instance count tag properly when empty
Handle instance count tag properly when empty

There are 3 states of `NumberOfSeriesRelatedInstances` in a C-FIND response that need to be handled.
- Tag is returned and populated
- Tag is returned and empty (orthanc)
- Tag is not returned (dcmqrscp)

Now the latter 2 are handled in the same manner.

scitran/reaper,scitran/reaper