Bug#26285 selecting information_schema crahes server

The crash happens when 'skip-grant-tables' is enabled.
We skip the filling of I_S privilege tables 
if acl_cache is not initialized.

mysql-test/r/skip_grants.result

@@ -58,3 +58,15 @@ DROP PROCEDURE p3;
 DROP FUNCTION f1;
 DROP FUNCTION f2;
 DROP FUNCTION f3;
+select count(*) from information_schema.COLUMN_PRIVILEGES;
+count(*)
+0
+select count(*) from information_schema.SCHEMA_PRIVILEGES;
+count(*)
+0
+select count(*) from information_schema.TABLE_PRIVILEGES;
+count(*)
+0
+select count(*) from information_schema.USER_PRIVILEGES;
+count(*)
+0

mysql-test/t/skip_grants.test

@@ -108,3 +108,11 @@ DROP PROCEDURE p3;
 DROP FUNCTION f1;
 DROP FUNCTION f2;
 DROP FUNCTION f3;
+
+#
+# Bug#26285 Selecting information_schema crahes server
+#
+select count(*) from information_schema.COLUMN_PRIVILEGES;
+select count(*) from information_schema.SCHEMA_PRIVILEGES;
+select count(*) from information_schema.TABLE_PRIVILEGES;
+select count(*) from information_schema.USER_PRIVILEGES;

sql/sql_acl.cc

@@ -5882,6 +5882,8 @@ int fill_schema_user_privileges(THD *thd, TABLE_LIST *tables, COND *cond)
   char *curr_host= thd->security_ctx->priv_host_name();
   DBUG_ENTER("fill_schema_user_privileges");
 
+  if (!initialized)
+    DBUG_RETURN(0);
   pthread_mutex_lock(&acl_cache->lock);
 
   for (counter=0 ; counter < acl_users.elements ; counter++)
@@ -5941,6 +5943,8 @@ int fill_schema_schema_privileges(THD *thd, TABLE_LIST *tables, COND *cond)
   char *curr_host= thd->security_ctx->priv_host_name();
   DBUG_ENTER("fill_schema_schema_privileges");
 
+  if (!initialized)
+    DBUG_RETURN(0);
   pthread_mutex_lock(&acl_cache->lock);
 
   for (counter=0 ; counter < acl_dbs.elements ; counter++)