WifiKeyStore: Handle existing config being null

This could be null when there is no existing config matching the added
config.

Bug: 144444818
Test: Verify the crash reported in the bug no longer occurs.
Change-Id: Ic08f3cf84360a9caf50be514a9920ec25163b1c8
1 file changed
tree: 9f0f9ee895f452b6e4ad4040ca16be8e403f1d9b
  1. service/
  2. PREUPLOAD.cfg