The wifi list is not null at no signal room

- check the wifi list's size for error message.
- fix the carrier's summary display "connect" at no signal room

Bug: 177390298
Test: atest ProviderModelSliceHelperTest
atest ProviderModelSliceTest

Change-Id: I692aadd01a290cce2438b0d3c084bef8d8d3fa24
2 files changed