main/sorcery: Don't fail object set creation from JSON if field fails

Some individual fields may fail their conversion due to their default
values being invalid for their custom handlers. In particular,
configuration values that depend on others being enabled (and thus have
an empty default value) are notorious for tripping this routine up. An
example of this are any of the DTLS options for endpoints. Any of the
DTLS options will fail to be applied (as DTLS is not enabled), causing
the entire object set to be aborted.

This patch makes it so that we log a debug message when skipping a
field, and rumble on anyway.

ASTERISK-25238

Change-Id: I0bea13de79f66bf9f9ae6ece0e94a2dc1c026a76