Query failed when updating existing host prototypes

 57058:20200430:143323.381 [Z3005] query failed: [0] PGRES_FATAL_ERROR:ERROR:  syntax error at or near "for"
LINE 1: select null from group_prototype where for update
                                               ^
 [select null from group_prototype where for update]

diff --git a/src/zabbix_server/lld/lld_host.c b/src/zabbix_server/lld/lld_host.c
index caa35e2581..4d48fa39fa 100644
--- a/src/zabbix_server/lld/lld_host.c
+++ b/src/zabbix_server/lld/lld_host.c
@@ -1532,11 +1532,14 @@ static void     lld_groups_save(zbx_vector_ptr_t *groups, const zbx_vector_ptr_t *gr
 
        DBbegin();
 
-       if (SUCCEED != DBlock_group_prototypeids(&new_group_prototype_ids))
+       if (0 != new_group_prototype_ids.values_num)
        {
-               /* the host group prototype was removed while processing lld rule */
-               DBrollback();
-               goto out;
+               if (SUCCEED != DBlock_group_prototypeids(&new_group_prototype_ids))
+               {
+                       /* the host group prototype was removed while processing lld rule */
+                       DBrollback();
+                       goto out;
+               }
        }
 
        if (0 != new_group_prototype_ids.values_num)