"method X cannot be accessed" error causes the tree to have an error symbol

If a method is not accessible, hyperlinking won't work. The type-checker won't assign the right symbol to the corresponding tree, even when there's no ambiguity.

```scala
package a {
  object A {
    protected[a] def foo() = ???
  }
}

package b {
  class B {
    a.A.foo() // method foo in object A cannot be accessed in object a.A 
  }
}
```

'foo' is assigned an error symbol.