Fail scan request if no channels are available

This fails scan request if no available channels could
be scanned for this request.
With this fix we can avoid the freezing of WifiScanner in
aformentioned case.

Bug: 67015387
Test: compile, unit test, integration test
Change-Id: I68654ce8d53104484c1559d8b0525585ab50b9e5
2 files changed