Fix NPE in escaping if output settings cloned twice

[TalgatAkhm]

Cloning OutputSettings leads to NPE during escaping
Code example:

    private static final Document.OutputSettings DEFAULT = new Document.OutputSettings();

    @Test
    public void test() {
        Entities.escape("text", DEFAULT.clone());
        Entities.escape("text", DEFAULT.clone());
    }

Stack:

java.lang.NullPointerException: Cannot invoke "org.jsoup.nodes.Entities$CoreCharset.ordinal()" because "charset" is null

  at org.jsoup@1.15.3/org.jsoup.nodes.Entities.canEncode(Entities.java:298)
  at org.jsoup@1.15.3/org.jsoup.nodes.Entities.escape(Entities.java:239)
  at org.jsoup@1.15.3/org.jsoup.nodes.Entities.escape(Entities.java:145)

[jhy]

Thanks, merged!