Fix auto argument passing for more auto arguments than formals

The change in 626200713bb3cc844a9feb6af583c9b6b42c6dbc didn't account
for when the number of auto arguments is bigger than the number of
formal arguments. This causes the following:

  $ nix-instantiate --eval -E '{ ... }@args: args.foo' --argstr foo foo
  nix-instantiate: src/libexpr/attr-set.hh:55: void nix::Bindings::push_back(const nix::Attr&): Assertion `size_ < capacity_' failed.
  Aborted (core dumped)

0 files changed, 0 insertions, 0 deletions