PSFTP: make the 'close' subcommand return success.

A user points out that it always returned failure, even if it
succeeded. As a result, a 'psftp -b' script of the form

  open this.host
  do stuff
  close
  open that.host
  do stuff
  close

would terminate at the first 'close', believing it to have failed, and
PSFTP would exit with a failure status.

(Not only that, but there would be no error message indicating _why_
PSFTP had closed, because when a command returns failure it's expected
to have printed an error message already.)

psftp.c

@@ -1024,7 +1024,7 @@ int sftp_cmd_close(struct sftp_command *cmd)
     }
     do_sftp_cleanup();
 
-    return 0;
+    return 1;
 }
 
 void list_directory_from_sftp_warn_unsorted(void)