Merge pull request ruby-ldap#67 from equinux/catch_converter_not_found_error

Catch Encoding::ConverterNotFoundError

Author: Rory O'Connell

lib/net/ber/core_ext/string.rb

@@ -32,6 +32,8 @@ def raw_utf8_encoded
         self.encode('UTF-8').force_encoding('ASCII-8BIT')
       rescue Encoding::UndefinedConversionError
         self
+      rescue Encoding::ConverterNotFoundError
+        return self
       end
     else
       self