BUG: FastByteArrayOutputStream.write(byte[],int,int) can fail to move position

[magicprinc]

@Test
void _bug_write_array0 () {
  val o = new it.unimi.dsi.fastutil.io.FastByteArrayOutputStream ();
  o.write(new byte[]{1,2,3,4,5});
  assertEquals(5, o.length());
  assertEquals(5, o.position());

  o.position(0);
  o.write(new byte[]{1,2,3});
  assertEquals(5, o.length());
  assertEquals(0, o.position());//!!! MUST be 3: 0+3
}

fix

@Override
public void write (byte[] b, int off, int len) {
  ByteArrays.ensureOffsetLength(b, off, len);
  if (position + len > buf.length)
      buf = ByteArrays.grow(buf, position + len, position);
  System.arraycopy(b, off, buf, position, len);
  position += len;
  if (count < position) count = position;
}

PS: please also see my PR #360 with useful extra functionality