message: adjust for get_fn signature change
diff: @@ -338,7 +338,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
  // vtable_ptr: *mut usize,
  // ) -> u32
  // We abort on panic, so not much is going on here, but we still have to call the closure.
  - let f = this.read_scalar(args[0])?.to_ptr()?;
  + let f = this.read_scalar(args[0])?.not_undef()?;
  let data = this.read_scalar(args[1])?.not_undef()?;
  let f_instance = this.memory().get_fn(f)?.as_instance()?;
  this.write_null(dest)?;
  