libcli/security: claims_conversions: check for NULL in claims array
If by mistake we end up with a NULL in our array of claims pointers,
it is better to return an error than crash.
There can be NULLs in the array if a resource attribute ACE has a
claim that uses 0 as a relative data pointer. Samba assumes this means
a NULL pointer, rather than a zero offset.
Credit to OSS-Fuzz.
REF: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=66777
BUG: https://bugzilla.samba.org/show_bug.cgi?id=15606
Signed-off-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>