Searching for invalid setting results in search field being removed

REGRESSION: Yes
WORKING: 3112924 (UE4/Main)
BROKEN: 3160080 (UE4/Release-4.14)

If the user searches for something that produces no results, the search field will disappear and the user cannot clear it. They will have to close and reopen the panel to get the settings back.

This has been seen in multiple areas of the editor (Persona, level editor, material editor).

1. Open QAGame in editor.
2. Select the Floor mesh.
3. In the Details panel, search for something that's not in that panel (or search random letters).

RESULT:

The Details panel clears out and the search field is removed.