Add tests for PL/pgSQL returning unnamed portals as refcursor

Existing tests only covered returning explicitly named portals as
refcursor.  The unnamed cursor case was recently broken without a test
failing.

src/test/regress/expected/plpgsql.out

@@ -2242,6 +2242,30 @@ drop function sp_id_user(text);
 --
 create table rc_test (a int, b int);
 copy rc_test from stdin;
+create function return_unnamed_refcursor() returns refcursor as $$
+declare
+    rc refcursor;
+begin
+    open rc for select a from rc_test;
+    return rc;
+end
+$$ language plpgsql;
+create function use_refcursor(rc refcursor) returns int as $$
+declare
+    rc refcursor;
+    x record;
+begin
+    rc := return_unnamed_refcursor();
+    fetch next from rc into x;
+    return x.a;
+end
+$$ language plpgsql;
+select use_refcursor(return_unnamed_refcursor());
+ use_refcursor 
+---------------
+             5
+(1 row)
+
 create function return_refcursor(rc refcursor) returns refcursor as $$
 begin
     open rc for select a from rc_test;

src/test/regress/sql/plpgsql.sql

@@ -1910,6 +1910,28 @@ copy rc_test from stdin;
 500	1000
 \.
 
+create function return_unnamed_refcursor() returns refcursor as $$
+declare
+    rc refcursor;
+begin
+    open rc for select a from rc_test;
+    return rc;
+end
+$$ language plpgsql;
+
+create function use_refcursor(rc refcursor) returns int as $$
+declare
+    rc refcursor;
+    x record;
+begin
+    rc := return_unnamed_refcursor();
+    fetch next from rc into x;
+    return x.a;
+end
+$$ language plpgsql;
+
+select use_refcursor(return_unnamed_refcursor());
+
 create function return_refcursor(rc refcursor) returns refcursor as $$
 begin
     open rc for select a from rc_test;