Fix ICE on const of nullable enum with fields in null case.

That is, if you have an enum type that is subject to the nullable
pointer optimization, but the null variant has a nonzero number of
fields, and you declare a static whose value is of that variant, then
that used to be an ICE but this change fixes it.

src/librustc/middle/trans/adt.rs

@@ -730,7 +730,6 @@ pub fn trans_const(ccx: &CrateContext, r: &Repr, discr: Disr,
             if discr == nndiscr {
                 C_struct(build_const_struct(ccx, nonnull, vals), false)
             } else {
-                assert_eq!(vals.len(), 0);
                 let vals = nonnull.fields.iter().enumerate().map(|(i, &ty)| {
                     let llty = type_of::sizing_type_of(ccx, ty);
                     if i == ptrfield { C_null(llty) } else { C_undef(llty) }

src/test/run-pass/enum-nullable-const-null-with-fields.rs

@@ -0,0 +1,19 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use std::result::{Result,Ok};
+static C: Result<(), ~int> = Ok(());
+
+// This is because of yet another bad assertion (ICE) about the null side of a nullable enum.
+// So we won't actually compile if the bug is present, but we check the value in main anyway.
+
+pub fn main() {
+    assert!(C.is_ok());
+}