Fix generator-invocation legality check for varargs generators (#47739)
This code was introduced by me back in #31025 to speed up evaluation
of generated functions that didn't make use of all of their arguments to
make generation decisions. However, it neglected to take into account the
possibility that the generator could be varargs. As a result, an unfortunate
coincidence of an unused slot in the correct position could have allowed
expansion of generators that were not supposed to be expandable. This can
cause incorrect inference with all the usual consequences. However, fortunately
this coincidence appears to be pretty rare.
Fixes https://github.com/JuliaDebug/CassetteOverlay.jl/issues/12
julia
328dd578 - Fix generator-invocation legality check for varargs generators (#47739)
