Fix format string. Fixes #1109. Closes #1111

CHANGELOG

@@ -1,5 +1,8 @@
 #Nmap Changelog ($Id$); -*-text-*-
 
+o [NSE][GH#1111] Fix a script crash in ftp.lua when PASV connection timed out.
+  [Aniket Pandey]
+
 o [NSE][GH#1114] Update bitcoin-getaddr to receive more than one response
   message, since the first message usually only has one address in it. [h43z]
 

nselib/ftp.lua

@@ -276,7 +276,7 @@ function pasv(socket, buffer)
     end
   else
     if not code or code >= 300 then
-      return nil, ("PASV failed: %d %s"):format(code or "socket", message)
+      return nil, ("PASV failed: %s %s"):format(code or "socket", message)
     end
     -- Compute the PASV port as given by the server
     -- The server should answer with something like