Description: rxrpc: fix some null-ptr-deref bugs in server_key.c
References:
 https://bugzilla.redhat.com/show_bug.cgi?id=2083992
Notes:
 carnil> Fixes 12da59fcab5a ("rxrpc: Hand server key parsing off to the
 carnil> security class") in 5.11-rc1.
Bugs:
upstream: released (5.18-rc1) [ff8376ade4f668130385839cef586a0990f8ef87]
5.10-upstream-stable: N/A "Vulnerable code introduced later"
4.19-upstream-stable: N/A "Vulnerable code introduced later"
4.9-upstream-stable: N/A "Vulnerable code introduced later"
sid: released (5.17.3-1)
5.10-bullseye-security: N/A "Vulnerable code introduced later"
4.19-buster-security: N/A "Vulnerable code introduced later"
4.9-stretch-security: N/A "Vulnerable code introduced later"