BUG#9455 mysqladmin status crash the server

 - Send error to client when mysql_change_db fails.


sql/sql_db.cc:
  Added a note to comment for mysql_change_db that it will not send any error to the client.
sql/sql_parse.cc:
  Call net_send_error(thd) if mysql_change_db fails.
  Remove comments claiming that mysql_change_db sends error the the client.

sql/sql_db.cc

@@ -1009,6 +1009,9 @@ static long mysql_rm_arc_files(THD *thd, MY_DIR *dirp,
     replication slave SQL thread (for that thread, setting of thd->db is done
     in ::exec_event() methods of log_event.cc).
 
+    This function does not send the error message to the client, if that
+    should be sent to the client, call net_send_error after this function 
+
   RETURN VALUES
     0	ok
     1	error

sql/sql_parse.cc

@@ -260,13 +260,15 @@ int check_user(THD *thd, enum enum_server_command command,
   
 #ifdef NO_EMBEDDED_ACCESS_CHECKS
   thd->master_access= GLOBAL_ACLS;			// Full rights
-  /* Change database if necessary: OK or FAIL is sent in mysql_change_db */
+  /* Change database if necessary */
   if (db && db[0])
   {
     thd->db= 0;
     thd->db_length= 0;
     if (mysql_change_db(thd, db))
     {
+      /* Send the error to the client */
+      net_send_error(thd);
       if (thd->user_connect)
 	decrease_user_connections(thd->user_connect);
       DBUG_RETURN(-1);
@@ -395,11 +397,13 @@ int check_user(THD *thd, enum enum_server_command command,
 	  check_for_max_user_connections(thd, thd->user_connect))
 	DBUG_RETURN(-1);
 
-      /* Change database if necessary: OK or FAIL is sent in mysql_change_db */
+      /* Change database if necessary */
       if (db && db[0])
       {
         if (mysql_change_db(thd, db))
         {
+          /* Send error to the client */
+          net_send_error(thd);
           if (thd->user_connect)
             decrease_user_connections(thd->user_connect);
           DBUG_RETURN(-1);