code: static CoderResult overflow(CharBuffer input, int i, CharBuffer output, int j) {
          input.position(i - input.arrayOffset());
          output.position(j - output.arrayOffset());
          return CoderResult.OVERFLOW;
      }
docs: Internal helper method to properly position buffers after encoding up
  until an overflow.
  
  @param input the input buffer
  @param i the array offset in the input buffer (translated to position)
  @param output the output buffer
  @param j the array offset in the output buffer (translated to position)
  @return CoderResult.OVERFLOW