fix missing fcache when fmgr hook is called in unexpected order

expected/README

@@ -1,5 +1,7 @@
 plpgsql_check_passive.out			PostgreSQL 14, 15, 16
 plpgsql_check_passive_1.out			PostgreSQL 12, 13
+plpgsql_check_passive_2.out			PostgreSQL 18
 plpgsql_check_active_1.out			PostgreSQL 12, 13
 plpgsql_check_active_2.out			PostgreSQL 14, 15, 16
-plpgsql_check_active.out			PostgreSQL 17, 18
+plpgsql_check_active_3.out			PostgreSQL 18
+plpgsql_check_active.out			PostgreSQL 17

expected/plpgsql_check_active.out

@@ -9396,3 +9396,34 @@ set plpgsql_check.cursors_leaks to on;
 do $$ declare c cursor for select 1; begin open c; call p1(); end $$;
 set plpgsql_check.cursors_leaks to default;
 drop procedure p1;
+-- should not crash
+create or replace function nested_trace_test(a int)
+returns int as $$
+begin
+  perform plpgsql_check_pragma('enable:tracer');
+  return a + 1;
+end;
+$$ language plpgsql;
+create or replace function trace_test(b int)
+returns int as $$
+declare r int default 0;
+begin
+  for i in 1..b
+  loop
+    r := nested_trace_test(r);
+  end loop;
+  return r;
+end;
+$$ language plpgsql;
+-- when plpgsql_check is not loaded yet, then plpgsql_check is
+-- load by perform plpgsql_check_pragma and this is another
+-- case, when fmgr hook is not called in expected order.
+\c
+-- should not to crash
+select trace_test(3);
+WARNING:  late initialization of fmgr_plpgsql_cache
+ trace_test 
+------------
+          3
+(1 row)
+

expected/plpgsql_check_active_1.out

@@ -9398,3 +9398,34 @@ set plpgsql_check.cursors_leaks to on;
 do $$ declare c cursor for select 1; begin open c; call p1(); end $$;
 set plpgsql_check.cursors_leaks to default;
 drop procedure p1;
+-- should not crash
+create or replace function nested_trace_test(a int)
+returns int as $$
+begin
+  perform plpgsql_check_pragma('enable:tracer');
+  return a + 1;
+end;
+$$ language plpgsql;
+create or replace function trace_test(b int)
+returns int as $$
+declare r int default 0;
+begin
+  for i in 1..b
+  loop
+    r := nested_trace_test(r);
+  end loop;
+  return r;
+end;
+$$ language plpgsql;
+-- when plpgsql_check is not loaded yet, then plpgsql_check is
+-- load by perform plpgsql_check_pragma and this is another
+-- case, when fmgr hook is not called in expected order.
+\c
+-- should not to crash
+select trace_test(3);
+WARNING:  late initialization of fmgr_plpgsql_cache
+ trace_test 
+------------
+          3
+(1 row)
+

expected/plpgsql_check_active_2.out

@@ -9395,3 +9395,34 @@ set plpgsql_check.cursors_leaks to on;
 do $$ declare c cursor for select 1; begin open c; call p1(); end $$;
 set plpgsql_check.cursors_leaks to default;
 drop procedure p1;
+-- should not crash
+create or replace function nested_trace_test(a int)
+returns int as $$
+begin
+  perform plpgsql_check_pragma('enable:tracer');
+  return a + 1;
+end;
+$$ language plpgsql;
+create or replace function trace_test(b int)
+returns int as $$
+declare r int default 0;
+begin
+  for i in 1..b
+  loop
+    r := nested_trace_test(r);
+  end loop;
+  return r;
+end;
+$$ language plpgsql;
+-- when plpgsql_check is not loaded yet, then plpgsql_check is
+-- load by perform plpgsql_check_pragma and this is another
+-- case, when fmgr hook is not called in expected order.
+\c
+-- should not to crash
+select trace_test(3);
+WARNING:  late initialization of fmgr_plpgsql_cache
+ trace_test 
+------------
+          3
+(1 row)
+