Prevent AutoCompleteTextView from opening a popup when it shouldn't

Bug #5553515

The People app is forcing ACTV to show the IME which had the side effect
of showing the drop down popup. ACTV was unfortunately not ready to show
the drop down if the filtering resulted in no results. Doing so was putting
ACTV in a weird state that in turn caused a window to be leaked and really
bad behavior to occur in the lower graphics levels.

Change-Id: I2ff146d5ae4e4a28edf6ea17039c9f8fdb710e4f