Reject trailing separators in PointConverter

[rootvector2]

PointConverter.convertToType splits the inner coordinate string with POINT_SPLIT.split(coordinates), and String.split with the default limit drops trailing empty tokens. A trailing separator after the two coordinates is swallowed, so (100,200,) and (100,200,,) parse to Point(100,200). That is inconsistent with (100,), which is already rejected because it yields a single token.

Pass -1 as the split limit so trailing empties are kept and the existing xy.length != 2 check rejects the malformed input. Keeping the bound in the converter means every caller gets the same validation, and valid (x,y) forms are unchanged. Found while auditing the awt converters alongside ColorConverter.

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[garydgregory]

@rootvector2
Please see #419 (comment)