Auto merge of #29817 - michaelwoerister:mir-ty-closure-fields, r=nikomatsakis

Add a missing case in LvalueTy::projection_ty() that popped up earlier today.

cc @rust-lang/compiler @nikomatsakis

src/librustc_mir/tcx/mod.rs

@@ -79,6 +79,8 @@ pub fn projection_ty(self,
                             adt_def.struct_variant().fields[field.index()].ty(tcx, substs),
                         ty::TyTuple(ref tys) =>
                             tys[field.index()],
+                        ty::TyClosure(_, ref closure_substs) =>
+                            closure_substs.upvar_tys[field.index()],
                         _ =>
                             tcx.sess.bug(&format!("cannot get field of type: `{:?}`", ty)),
                     },