bugfix for #1375

libmysqld/lib_sql.cc:
  some programs check mysql_error for empty string
sql/log.cc:
  in embedded library these members can be NULL

libmysqld/lib_sql.cc

@@ -91,6 +91,8 @@ emb_advanced_command(MYSQL *mysql, enum enum_server_command command,
     memcpy(net->last_error, thd->net.last_error, sizeof(net->last_error));
     memcpy(net->sqlstate, thd->net.sqlstate, sizeof(net->sqlstate));
   }
+  else
+    net->last_error[0]= 0;
   mysql->warning_count= ((THD*)mysql->thd)->total_warn_count;
   return result;
 }

sql/log.cc

@@ -1586,8 +1586,8 @@ bool MYSQL_LOG::write(THD *thd,const char *query, uint query_length,
           tmp_errno=errno;
       }
       if (my_b_printf(&log_file, "# User@Host: %s[%s] @ %s [%s]\n",
-                      thd->priv_user,
-                      thd->user,
+                      thd->priv_user ? thd->priv_user : "",
+                      thd->user ? thd->user : "",
                       thd->host ? thd->host : "",
                       thd->ip ? thd->ip : "") == (uint) -1)
         tmp_errno=errno;