WifiScanningService: Handle getAvailableChannels() when scanner is off

Add a null check for channel helper to avoid a crash when we get the
call from the app when scanner is off (i.e when wifi & location is off).

Bug: 150334212
Test: Tested with ag/10433983 (with both wifi off & on)
Test: atest com.android.server.wifi.scanner
Change-Id: Id178bf5badebe8e7ee5695d1f8884409fb86a6e3
2 files changed
tree: b3e2d843b8a85b9b0d4ab70a062c2ca0e4383bca
  1. apex/
  2. service/
  3. PREUPLOAD.cfg