Completion incorrectly finds core context, not task context, with core flags

[bitprophet]

E.g. completing inv -c mycollection mytask - or inv --debug mytask - doesn't show mytask flags, but instead shows core flags, due to some issue with the partial parsing during completion.

Specifically, the partial parsing doesn't know what the core flags are for some reason, e.g. it starts off, looks at -c (or --debug or whatever), goes "dafuq is this?" and bails too early. What was expected, and what happens when core flags are not involved, is that this parsing step sees the task name, switches to its context, then bails on the partial flag.