RCFilters: Allow empty saved query

For this, we also need to check for saved query visibility on the
saved query model initialization, because since the model starts
its life all-empty, if the saved query is also all-empty, it will
not trigger any item updates on the main model.

Bonus: Actually check whether defaults are empty; there was a
typo and problem with the original test.

Bug: T172387
Change-Id: Ibc536b577e4c3abcc04fa229f9978b651b2f9e61