Use DDP._CurrentPublicationInvocation to get userId

[zimme]

Let's use DDP._CurrentPublicationInvocation to get the userId if it's available, otherwise fall back to the current method to be backwards-compatible.

Possible since meteor/meteor#8629.

[gregory]

it's crazy how much time code is spent in the try/catch - would be much more efficient to rely on DDP._CurrentMethodInvocation.get() || DDP._CurrentPublicationInvocation.get();

[zimme]

@gregory I would happily accept a PR for this =)

[gregory]

Thanks @zimme - Not a blocker, will try to find some time for this :)