Force ASCII when decoding numbers from unicode-escape

Author: msimacek

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/charset/PythonUnicodeEscapeCharsetDecoder.java

@@ -83,7 +83,7 @@ static CoderResult decodeHexUnicodeEscape(ByteBuffer source, CharBuffer target,
         source.get(numbuf, 0, count);
         int codePoint;
         try {
-            codePoint = Integer.parseInt(new String(numbuf, 0, count), 16);
+            codePoint = Integer.parseInt(new String(numbuf, 0, count, StandardCharsets.US_ASCII), 16);
         } catch (NumberFormatException e) {
             int pos = source.position();
             source.position(initialPosition);