Don't compute LastPrivate data for Def::Err.

Author: jseyfried

src/librustc_resolve/lib.rs

@@ -1047,6 +1047,7 @@ impl<'a> NameBinding<'a> {
 
     fn def_and_lp(&self) -> (Def, LastPrivate) {
         let def = self.def().unwrap();
+        if let Def::Err = def { return (def, LastMod(AllPublic)) }
         (def, LastMod(if self.is_public() { AllPublic } else { DependsOn(def.def_id()) }))
     }
 

src/test/compile-fail/import.rs

@@ -15,5 +15,10 @@ use zed::baz;
 
 mod zed {
     pub fn bar() { println!("bar"); }
+    use foo; //~ ERROR unresolved import
+}
+
+fn main() {
+    zed::foo(); // Check that this does not panic. Ideally, it would be a privacy error.
+    bar();
 }
-fn main() { bar(); }