FCPInterface.handleGetIdentities(): 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
FCPInterface.handleGetTrusts(): 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.handleGetTrusts(): 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