Fixed the incorrect roaming override

If the empty string is in the roaming override resource overlay,
it might incorrectly override the roaming state.

Test: Manual
bug: 63687431
Merged-In: I6629b2b4815f6740ada4bd0a69eb2bf8829db1fc
Change-Id: I6629b2b4815f6740ada4bd0a69eb2bf8829db1fc