Problem:     on malformed message is_CLASS function crashes on assert.
Problem:
    on malformed message is_CLASS function crashes on assert.

Solution:
    check whether frame is extracted

bkmit/zproto,asokoloski/zproto,bkmit/zproto,sappo/zproto,somdoron/zproto,c-rack/zproto,somdoron/zproto,sphaero/zproto,sappo/zproto,jdiez17/zproto,zeromq/zproto,bkmit/zproto,somdoron/zproto,jemc/zproto,asokoloski/zproto,hintjens/zproto,jdiez17/zproto,zeromq/zproto,vyskocilm/zproto,jemc/zproto,c-rack/zproto,sphaero/zproto,hintjens/zproto,sappo/zproto,hintjens/zproto,jdiez17/zproto,bkmit/zproto,vyskocilm/zproto,jdiez17/zproto,jemc/zproto,hintjens/zproto,sappo/zproto,zeromq/zproto,zeromq/zproto,somdoron/zproto,jdiez17/zproto,sphaero/zproto,hintjens/zproto,asokoloski/zproto,asokoloski/zproto,sappo/zproto,hintjens/zproto,vyskocilm/zproto,bkmit/zproto,jemc/zproto,bkmit/zproto,c-rack/zproto,sappo/zproto,hintjens/zproto,zeromq/zproto,sappo/zproto,somdoron/zproto,jemc/zproto,vyskocilm/zproto,sphaero/zproto,c-rack/zproto,jemc/zproto,jemc/zproto,asokoloski/zproto,jdiez17/zproto,somdoron/zproto,vyskocilm/zproto,sphaero/zproto,vyskocilm/zproto,vyskocilm/zproto,sphaero/zproto,zeromq/zproto,zeromq/zproto,c-rack/zproto,c-rack/zproto,jdiez17/zproto,somdoron/zproto,asokoloski/zproto,asokoloski/zproto,bkmit/zproto,c-rack/zproto