net/sctp: fix a null dereference in sctp_disposition sctp_sf_do_5_1D_ce()

In the Linux kernel, the following vulnerability has been resolved: net/sctp: fix a null dereference in sctp_disposition sctp_sf_do_5_1D_ce() If new_asoc->peer.adaptation_ind=0 and sctp_ulpevent_make_authkey=0 and sctp_ulpevent_make_authkey() returns 0, then the variable ai_ev remains zero and the zero will be dereferenced in the sctp_ulpevent_free() function.