fix handling of "Wrong domain name" error

If no endpoint was found, assert that the cause code indicates error, so that
the remaining code path doesn't assume finding an endpoint was successful.

Also fix find_endpoint() to return an error cause (not 0) in case it finds the
domain name to be wrong.

After this, the error described in OS#3488 simply results in a CRCX failure,
not in a program crash.

Related: OS#3488
Change-Id: I87e2d76c22603d6fef89907c3cf8f7965abf35a0
1 file changed