Field queries with empty text in advanced search produce multiple results

[amir-zeldes]

if no text is specified, but a field is selected, matches are listed under multiple rubrics, e.g.:

http://data.copticscriptorium.org/search?text=&translation=Anthony+Alcock

[amir-zeldes]

Comment from @lgessler

it looks like we missed this corner case (special metadatum chosen and no freetext supplied) while we were testing. Probably the sensible thing to do here is to short-circuit the freetext matching logic in case it's empty