account for public only credentials in #to_s

SNMP in particular will only have a public, so we need
to account for this so we don't output poorly formed text
with a trailing ':' char

5266

lib/metasploit/framework/credential.rb

@@ -75,8 +75,10 @@ module Metasploit
       def to_s
         if realm && realm_key == Metasploit::Model::Realm::Key::ACTIVE_DIRECTORY_DOMAIN
           "#{self.realm}\\#{self.public}:#{self.private}"
-        else
+        elsif self.private
           "#{self.public}:#{self.private}#{at_realm}"
+        else
+          self.public
         end
       end
 

lib/msf/core/auxiliary/auth_brute.rb

@@ -566,7 +566,6 @@ module Auxiliary::AuthBrute
     else
       level = opts[:level].to_s.strip
     end
-
     host_ip = opts[:ip] || opts[:rhost] || opts[:host] || (rhost rescue nil) || datastore['RHOST']
     host_port = opts[:port] || opts[:rport] || (rport rescue nil) || datastore['RPORT']
     msg = opts[:msg] || opts[:message] || opts[:legacy_msg]