ill-typed AIR code, when using reveal

[zeldovich]

The following code:

use vstd::prelude::*;

verus! {
    proof fn p() {
        assert(Seq::<int>::empty().to_multiset().len() == 0);
        reveal(Seq::to_multiset);
    }
}

crashes with:

thread '<unnamed>' panicked at rust_verify/src/verifier.rs:780:21:
internal error: generated ill-typed AIR code: error 'error 'use of undeclared variable fuel%vstd!seq_lib.impl&%0.to_multiset.' in expression 'fuel%vstd!seq_lib.impl&%0.to_multiset.'' in expression '(fuel_bool fuel%vstd!seq_lib.impl&%0.to_multiset.)'
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
thread '<unnamed>' panicked at rust_verify/src/verifier.rs:2110:29:
worker thread panicked