btm_process_remote_ext_features: return if no record

It's not possible that we don't have a security when we receive remote
ext features, because we create a record upon ACL connection.  Not
possible for direct bonding as well.

Bug: 159815595
Tag: #refactor
Test: compile & verify basic functions working
Change-Id: I70313e7e34d72741826f712baeccc4bdcb531757