Fixed the has_datespan calculation in reports
Fixed the has_datespan calculation in reports

It would error if the filter was an explicit reference to a field and
not a string reference.

dimagi/commcare-hq,gmimano/commcaretest,dimagi/commcare-hq,puttarajubr/commcare-hq,puttarajubr/commcare-hq,SEL-Columbia/commcare-hq,SEL-Columbia/commcare-hq,dimagi/commcare-hq,gmimano/commcaretest,qedsoftware/commcare-hq,puttarajubr/commcare-hq,gmimano/commcaretest,qedsoftware/commcare-hq,puttarajubr/commcare-hq,dimagi/commcare-hq,qedsoftware/commcare-hq,qedsoftware/commcare-hq,dimagi/commcare-hq,SEL-Columbia/commcare-hq,qedsoftware/commcare-hq