This bug checks the fix for golang/go#66250. Package references should not
crash when one package file lacks a package name.

TODO(rfindley): the -ignore_extra_diags flag is only necessary because of
problems matching diagnostics in the broken file, likely due to poor parser
recovery.

-- flags --
-ignore_extra_diags

-- a.go --
package x //@refs("x", "x")

-- b.go --

func _() {
}