Don't crash on unknown incoming Jingle actions.
Don't crash on unknown incoming Jingle actions.

Previously, gabble_jingle_session_parse() called produce_action() (which
asserts if you pass it JINGLE_ACTION_UNKNOWN) before checking whether
the action is UNKNOWN, with hilarious consequences.

Fixes: fd.o#20807

jku/telepathy-gabble,Ziemin/telepathy-gabble,Ziemin/telepathy-gabble,mlundblad/telepathy-gabble,community-ssu/telepathy-gabble,mlundblad/telepathy-gabble,jku/telepathy-gabble,community-ssu/telepathy-gabble,community-ssu/telepathy-gabble,Ziemin/telepathy-gabble,community-ssu/telepathy-gabble,mlundblad/telepathy-gabble,Ziemin/telepathy-gabble,jku/telepathy-gabble