[Minor] rspamc: fix crash on non-string element in messages

[fatalbanana]

Lists and dictionaries can be added to the protocol response inside messages, e.g.

          task:append_message({foo = 'bar'}, 'yolo')
          task:append_message({'bar','foo'}, 'swag')

Currently this is causing a crash in rspamc.

(gdb) p ucl_object_tostring(cmesg)
$3 = 0x0

This doesn't look quite as I might have imagined it but it's better than crashing:

Message - yolo: object
Message - swag: array

[fatalbanana]

the patch as currently proposed mishandles strings. :\ I'll revisit.

[fatalbanana]

Grr, I was using a wrong API in testing (set_message where I meant append_message). :/ This is OK ...

[vstakhov]

I don't like the usage of the ucl_object_tostring_forced here, as it is way too bogus. For a human readable implementation I would suggest just to emit ucl object into, well, ucl. ucl_object_tostring_forced was designed to do something similar but in a more intrusive and state modifying way: deconst->trash_stack[UCL_TRASH_VALUE] = ucl_object_emit_single_json (obj);. Please note that it also emits json instead of a more logical choice of the UCL_EMIT_CONFIG (at least for the human readable output).

[fatalbanana]

Message - yolo: {"foo":"bar"}
Message - swag: ["bar","foo"]
Message - barf: lol

looks nicer

[fatalbanana]

Using UCL_EMIT_CONFIG as suggested:

Message - yolo: foo = "bar";

Message - swag: [
    "bar",
    "foo",
]

looks worse to me.

[vstakhov]

Ok, let's go with the JSON approach, but please read my other comments.

[fatalbanana]

Message - yolo: {"foo":"bar"}
Message - swag: ["bar","foo"]
Message - long: ["long","long","long","long","long","long","long","long","lo
Message - barf: lol