We cannot enforce that the RNP library is available at runtime, because we're using js-ctypes.

We should try to avoid that the OpenPGP related UI is shown, and gives the user a false impression regarding using encryption.

I have an initial patch that avoids the most obvious things.

We might want revisit this at a later time, e.g. if preferences say "require encryption" but we cannot send encrypted. In this scenario we need to ensure that we don't send.

Also, I'll optimize the console statements we give when attempting to load the RNP and OTR libraries. I'll limit it to one statement about the success or failure.

Pushed by kaie@kuix.de:
https://hg.mozilla.org/comm-central/rev/00561da9004e
Fail gracefully if RNP library cannot be loaded. r=mkmelin