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

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AZL-60389 CVE-2025-32913 affecting package libsoup for versions less than 3.0.4-3

A flaw was found in libsoup, where the soupmessageheadersgetcontentdisposition function is vulnerable to a NULL pointer dereference. This flaw allows a malicious HTTP peer to crash a libsoup client or server that uses this function...