In recordExtensionInitPriv(), keep the scan til we're done with it

For reasons of sheer brain fade, we (I) was calling systable_endscan()
immediately after systable_getnext() and expecting the tuple returned
by systable_getnext() to still be valid.

That's clearly wrong.  Move the systable_endscan() down below the tuple
usage.

Discovered initially by Pavel Stehule and then also by Alvaro.

Add a regression test based on Alvaro's testing.

src/backend/catalog/aclchk.c

@@ -5283,8 +5283,6 @@ recordExtensionInitPriv(Oid objoid, Oid classoid, int objsubid, Acl *new_acl)
 	/* There should exist only one entry or none. */
 	oldtuple = systable_getnext(scan);
 
-	systable_endscan(scan);
-
 	/* If we find an entry, update it with the latest ACL. */
 	if (HeapTupleIsValid(oldtuple))
 	{
@@ -5340,6 +5338,8 @@ recordExtensionInitPriv(Oid objoid, Oid classoid, int objsubid, Acl *new_acl)
 		CatalogUpdateIndexes(relation, tuple);
 	}
 
+	systable_endscan(scan);
+
 	/* prevent error when processing objects multiple times */
 	CommandCounterIncrement();
 

src/test/modules/test_extensions/Makefile

@@ -3,11 +3,11 @@
 MODULE = test_extensions
 PGFILEDESC = "test_extensions - regression testing for EXTENSION support"
 
-EXTENSION = test_ext1 test_ext2 test_ext3 test_ext4 test_ext5 \
+EXTENSION = test_ext1 test_ext2 test_ext3 test_ext4 test_ext5 test_ext6 \
 			test_ext_cyclic1 test_ext_cyclic2
 DATA = test_ext1--1.0.sql test_ext2--1.0.sql test_ext3--1.0.sql \
-	   test_ext4--1.0.sql test_ext5--1.0.sql test_ext_cyclic1--1.0.sql \
-	   test_ext_cyclic2--1.0.sql
+	   test_ext4--1.0.sql test_ext5--1.0.sql test_ext6--1.0.sql \
+	   test_ext_cyclic1--1.0.sql test_ext_cyclic2--1.0.sql
 
 REGRESS = test_extensions test_extdepend
 

src/test/modules/test_extensions/expected/test_extensions.out

@@ -35,3 +35,6 @@ drop cascades to extension test_ext5
 drop cascades to extension test_ext2
 drop cascades to extension test_ext4
 drop cascades to extension test_ext1
+CREATE EXTENSION test_ext6;
+DROP EXTENSION test_ext6;
+CREATE EXTENSION test_ext6;

src/test/modules/test_extensions/sql/test_extensions.sql

@@ -13,3 +13,7 @@ SELECT extname, nspname, extversion, extrelocatable FROM pg_extension e, pg_name
 CREATE EXTENSION test_ext_cyclic1 CASCADE;
 
 DROP SCHEMA test_ext CASCADE;
+
+CREATE EXTENSION test_ext6;
+DROP EXTENSION test_ext6;
+CREATE EXTENSION test_ext6;

src/test/modules/test_extensions/test_ext6--1.0.sql

+grant usage on schema @extschema@ to public;

src/test/modules/test_extensions/test_ext6.control

+comment = 'test_ext6'
+default_version = '1.0'
+relocatable = false
+superuser = true
+schema = 'test_ext6'