Class ZCL_MQTT_PACKET_CONNECT constructor issue

[nomssi]

In constructor
mv_password = iv_password.
fails because of the implicit convertion String -> XString

[larshp]

thanks, pull requests welcome

[nomssi]

will create one (eventually) but first the fix:

1. in ZCL_MQTT_PACKET_CONNECT constructor:
   mv_password = cl_binary_convert=>string_to_xstring_utf8( CONV #( iv_password ) ).
2. in ZIF_MQTT_PACKET~ENCODE( )
   IF NOT mv_password IS INITIAL.
   lv_length = xstrlen( mv_password ). " <-- fix, was xstrlen( ms_will_message-message ).