Stim lists with no stim items not handled correctly

[zduey]

There is a bug in how the ratio of stimulated items to total possible stim items is calculated in the "Stimulation Parameter Summary" table in the case where there is a stim list has no stim items. The stim_params field in the json structure is used to determine what parameters were used within a given list in order to handle FR6/catFR6 where the stimulation targets can change from list to list. However, if the list has no stim items, then this stim_params field is empty for the entire list and therefore the words from that list are not counted towards the overall total.

@aliixuu