FCPInterface.handlePluginFCPMessage(): Fix using variable for wrong
return type
FCPInterface.handleGetScores(): Fix sending reply messages as
non-reply

- FCPPluginMessage.construct() is for non-reply mesages, it must not
be used when replying to something. See its JavaDoc
FCPInterface.handleGetScores(): Rename local variable to match content

- It can be a non-reply message when sending due to an event, not
due to a client message