Bug #17485: mysql client crashes when connecting to the Instance Manager

  Using \U or \u in a prompt with the mysql command-line client could
  crash when connecting to the instance manager, since it does not return
  information about the user when asked by the client. This is fixed by
  having the client use what it knowns about the user (or giving up and
  saying "(unknown)").

client/mysql.cc

@@ -3623,12 +3623,14 @@ static const char* construct_prompt()
       case 'U':
 	if (!full_username)
 	  init_username();
-	processed_prompt.append(full_username);
+        processed_prompt.append(full_username ? full_username :
+                                (current_user ?  current_user : "(unknown)"));
 	break;
       case 'u':
 	if (!full_username)
 	  init_username();
-	processed_prompt.append(part_username);
+        processed_prompt.append(part_username ? part_username :
+                                (current_user ?  current_user : "(unknown)"));
 	break;
       case PROMPT_CHAR:
 	processed_prompt.append(PROMPT_CHAR);