If message becomes nil, we should force a to_s for the regex

next_message can be nil sometimes if packet is nil (see net/ssh's
poll_message source)

Author: sinn3r

modules/exploits/unix/ssh/tectia_passwd_changereq.rb

@@ -146,7 +146,7 @@ def is_passwd_method?(user, transport)
 		message = transport.next_message
 
 		# Type 51 means the server is trying to tell us what auth methods are allowed.
-		if message.type == 51 and message !~ /password/
+		if message.type == 51 and message.to_s !~ /password/
 			print_error("#{rhost}:#{rport} - This host does not use password method authentication")
 			return false
 		end