Validate code point range in NumericEntityUnescaper.translate()

[dxbjavid]

Noticed translate calls Character.toChars(entityValue) for values above 0xFFFF without checking the upper code point bound, so a numeric reference like � (or �) throws IllegalArgumentException instead of being left alone. unescapeHtml4 and unescapeXml run this over untrusted markup, where every other malformed entity is silently ignored. Reject out-of-range code points the same way, by returning 0.

[garydgregory]

@vid
Again, your PR lacks a unit test. Let's save a round of interaction and do make sure you provide one on the first go around.

[dxbjavid]

Added testOutOfRangeCodePoint to NumericEntityUnescaperTest covering �, � and �. They're now left untranslated instead of throwing. Pushed.

[dxbjavid]

Thanks for the review and merge! Appreciated