skip checking any assertions if nothing has been claimed

[hawkrives]

This is not a performance optimization; instead, this ensures that less-than assertions don't turn green when there's nothing for them to assert against.

For example:

Requirement: Performance Studies [needs-more-items]
    [needs-more-items] Given all 0 courses matching subject == MUSPF and credits == 1.0 and level ∈ [100, 200] and name == '' and institution == STOLAF
        There must be:
          - count(terms) ≥ 6 [empty]
          - count(terms) where level == 100 ≤ 4 [done]

when in fact we would expect

Requirement: Performance Studies [needs-more-items]
    [needs-more-items] Given all 0 courses matching subject == MUSPF and credits == 1.0 and level ∈ [100, 200] and name == '' and institution == STOLAF
        There must be:
          - count(terms) ≥ 6 [empty]
          - count(terms) where level == 100 ≤ 4 [empty]

since there were no courses matching the filter.

[hawkrives]

I tagged as question because I don't remember if I've done this or not, yet.