Fix a crash caused by SIP addresses containing "%40" instead of "@"

CallerInfo.doSecondaryLookupIfNecessary() was assuming that SIP addresses
would always contain the character '@', but that's not always true since
the username/domainname delimiter can actually be "%40" (the URI-escaped
equivalent.)

This would cause the in-call UI to crash if you ever called a SIP address
like "xyz%40example.com".

TESTED:
 - Make an outgoing call to the SIP address "xyz%40example.com"
   ==> The call ultimately fails, but the in-call UI no longer crashes when
       it first comes up.

Bug: 5637074
Change-Id: I62d15a7ccd509924d38b780b92e657b9efa26125