Prevent non-blocking whitespaces from showing up in search

When search results use the placeholder summary text,
it becomes non-breaking whitespace. If that is the
summary, set the visibility to gone.

Change-Id: Ic3987a0990c33b6cc5aabffa0782ece6c553784a
Merged-In: Ifefa785b6c56d56da73ca78d874f46efcb9e991f
Fixes: 38029215
Test: make RunSettingsRoboTests