Fix DreamBackendTest

In the test, getStringArray is currently returning null which is causing
a null pointer exception. This only happens in testing when we mock
Resources, and it cannot return null in prod.

Test: atest SettingsLibRoboTests:DreamBackendTest
Change-Id: I8d7e21e26d3d786fce977c530f7537c549a1b678
1 file changed