Correctly handle paths from foreign items

tests/rustdoc-js/full-path-function.rs

@@ -12,5 +12,6 @@ pub mod b {
         pub fn len(&self) -> usize { 0 }
         pub fn bar(&self, w: u32) -> usize { 0 }
         pub fn bar2(&self, w: u32) -> u32 { 0 }
+        pub fn string(w: String) -> u32 { 0 }
     }
 }