Fix EVENT_SET_NULL_CIPHER_AND_INTEGRITY_DONE Error Handling

The Require Encryption toggle was appearing in the Settings
app because `mIsNullCipherAndIntegritySupported` was being
set to `true` when an exception other than REQUEST_NOT_SUPPORTED
was returned. The code was operating under the false assumption
that the only exception returned when a modem operation is not
supported was REQUEST_NOT_SUPPORTED, but other exceptions are
possible, like RADIO_NOT_AVAILABLE.

This change enforces that the only way to set
`mIsNullCipherAndIntegritySupported` to `true` is by receiving
an error free response from the RIL.

Bug: 294037720
Test: atest GsmCdmaPhoneTest
Change-Id: Ic5ffb09e6a30c42e594ff3bfea29f6c04f8b949d