CDM isDeviceAssociatedForWifiConnection returns false if no devices associated

The expectation is that when a caller holds COMPANION_APPROVE_WIFI_CONNECTIONS permisison,
isDeviceAssociatedForWifiConnection should always return true. In the
previous case, at least one device had to exist for this to be the case.

Bug: b/150459257
Test: A CTS test is what discovered the bug, and will be checked in
alongside this change.

Change-Id: If0a4dd427ebd437d7cd29810a26301b581ee3c75