It doesn't make sense to have an active selection while you are
filtering by entering text. You should be in one of two states:
1. Tabbing through completions (valid selection)
2. Entering a filter pattern (invalid selection)
Fixes#2843, where a crash would occur after the following:
1. tab to an item other than the first
2. <backspace>
3. re-type last character
4. <ctrl-d>
This would try to delete an out of range index.
b61691684e