code: protected BytesBuff ensureCapacity(int addBytes) {
  		if (addBytes < 0) {
  			throw new IllegalArgumentException(String.format("addBytes: %d (expected: >= 0)", addBytes));
  		}
  		ensureCapacityUnsafe(addBytes);
  		return this;
  	}
docs: 保证缓冲区大小
  @param addBytes 增加的字节数组长度
  
  @return 返回当前buff