[BUG] Key error when saving relation search target without articulators specified

[gracemyz]

Create a relation target where one or both hands has no articulator specified. Upon saving, get_path_abbrev() throws an error.

[gracemyz]

In the main corpus window, it's not possible to save a Relation module without specifying both articulators, so the displaystr() functions for RelationX and RelationY were returning bad values when faced with Relation Search Targets with missing articulators.