[PATCH] Issue 5418 - Sync_repl may crash while managing invalid cookie (#5420)

[PATCH] Issue 5418 - Sync_repl may crash while managing invalid cookie (#5420)

Bug description:
        If the servers receives an invalid cookie without separator '#',
        it parses it into an empty cookie (Sync_Cookie) instead of a NULL
        cookie (failure).
        Later it sigsegv when using the empty cookie.

Fix description:
        If the parsing fails return NULL

relates: #5418

Reviewed by: Viktor Ashirov, Mark Reynolds, William Brown, Simon Pichugin (thanks !)

Gbp-Pq: Name CVE-2022-2850.patch