Fixed NPE on StrictMode.setVmPolicy

There was an NPE on StrictMode.setVmPolicy, which I fixed just by ignoring setting the policy.
The fix might be a kind of overkill since the NPE actually happens because the `mQueue` on the line [1478](http://grepcode.com/file/repo1.maven.org/maven2/org.robolectric/android-all/4.3_r2-robolectric-0/android/os/StrictMode.java#1478) of `StrictMode.java` is null, however, I don't understand why it has been shadowed that way. Although, ignoring NPE still might be okay for testing purposes.