Added case for when impl generic associated type has a where clause

src/test/ui/rfc1598-generic-associated-types/generic-associated-types-where.rs

@@ -20,6 +20,7 @@ use std::fmt::{Display, Debug};
 trait Foo {
     type Assoc where Self: Sized;
     type Assoc2<T> where T: Display;
+    type Assoc3<T>;
     type WithDefault<T> where T: Debug = Iterator<Item=T>;
     type NoGenerics;
 }
@@ -29,6 +30,7 @@ struct Bar;
 impl Foo for Bar {
     type Assoc = usize;
     type Assoc2<T> = Vec<T>;
+    type Assoc3<T> where T: Iterator = Vec<T>;
     type WithDefault<'a, T> = &'a Iterator<T>;
     //~^ ERROR undeclared lifetime
     type NoGenerics = ::std::cell::Cell<i32>;