BUG #14928: Unchecked SearchSysCacheCopy1() return value

The following bug has been logged on the website:

Bug reference:      14928
Logged by:          Pan Bian
Email address:      bianpan2016@163.com
PostgreSQL version: 10.1
Operating system:   Linux
Description:

File: postgresql-10.1/src/backend/commands/tablecmds.c
Function: ATExecDetachPartition
Line: 13816

Function SearchSysCacheCopy1() may return a NULL pointer if there is no
enough memory. But in function ATExecDetachPartition(), its return value is
not checked, which may result in NULL dereference (see line 13818).

For your convenience, I copy and paste related codes as follows.

13815     classRel = heap_open(RelationRelationId, RowExclusiveLock);
13816     tuple = SearchSysCacheCopy1(RELOID,
13817
ObjectIdGetDatum(RelationGetRelid(partRel)));
13818     Assert(((Form_pg_class) GETSTRUCT(tuple))->relispartition);
13819 
13820     (void) SysCacheGetAttr(RELOID, tuple,
Anum_pg_class_relpartbound,
13821                            &isnull);
13822     Assert(!isnull);

Thank you!

Pan Bian