MDEV-7186 get_lock() crashes on Windows, main.sp_notembedded and...

MDEV-7186 get_lock() crashes on Windows, main.sp_notembedded and main.trigger_notembedded fail in buildbot

user locks are not affected by lowed_case_table_names

sql/mdl.h

@@ -351,7 +351,7 @@ class MDL_key
                                           NAME_LEN) - m_ptr + 1);
     m_hash_value= my_hash_sort(&my_charset_bin, (uchar*) m_ptr + 1,
                                m_length - 1);
-    DBUG_ASSERT(ok_for_lower_case_names(db));
+    DBUG_ASSERT(mdl_namespace == USER_LOCK || ok_for_lower_case_names(db));
   }
   void mdl_key_init(const MDL_key *rhs)
   {