message: Update Utf8.java: more detailed exception message
  Provide more detailed exception message for malformed 2 byte utf8 character
diff: @@ -110,9 +110,11 @@ public abstract class Utf8 {
  throws IllegalArgumentException {
  // Simultaneously checks for illegal trailing-byte in leading position (<= '11000000') and
  // overlong 2-byte, '11000001'.
  - if (byte1 < (byte) 0xC2
  - || isNotTrailingByte(byte2)) {
  - throw new IllegalArgumentException("Invalid UTF-8");
  + if (byte1 < (byte) 0xC2) {
  + throw new IllegalArgumentException("Invalid UTF-8: Illegal leading byte in 2 bytes utf");
  + }
  + if (isNotTrailingByte(byte2)) {
  + throw new IllegalArgumentException("Invalid UTF-8: Illegal trailing byte in 2 bytes utf");
  }
  resultArr[resultPos] = (char) (((byte1 & 0x1F) << 6) | trailingByteValue(byte2));
  }
  