[PATCH][BUG FIX] Unsafe access pointers.

Hi,
Last time, I promise.

It's probably not happening, but it can happen, I think.

Best regards.
Ranier Vilela

--- \dll\postgresql-12.0\a\backend\access\brin\brin_validate.c Mon Sep 30 17:06:55 2019
+++ brin_validate.c Fri Nov 15 08:14:58 2019
@@ -57,8 +57,10 @@

/* Fetch opclass information */
classtup = SearchSysCache1(CLAOID, ObjectIdGetDatum(opclassoid));
- if (!HeapTupleIsValid(classtup))
+ if (!HeapTupleIsValid(classtup)) {
elog(ERROR, "cache lookup failed for operator class %u", opclassoid);
+ return false;
+ }
classform = (Form_pg_opclass) GETSTRUCT(classtup);

opfamilyoid = classform->opcfamily;
@@ -67,8 +69,11 @@

/* Fetch opfamily information */
familytup = SearchSysCache1(OPFAMILYOID, ObjectIdGetDatum(opfamilyoid));
- if (!HeapTupleIsValid(familytup))
+ if (!HeapTupleIsValid(familytup)) {
elog(ERROR, "cache lookup failed for operator family %u", opfamilyoid);
+ ReleaseSysCache(classtup);
+ return false;
+ }
familyform = (Form_pg_opfamily) GETSTRUCT(familytup);

opfamilyname = NameStr(familyform->opfname);