fix align check for 2019.4.x

[AXiX-official]

prev impl has problem with uncompressed blocksInfo, if blocksInfo is not compressed, align_data may contains part of 16-bytes data hash on the beginning of uncompressed blocksInfo data. and wich would be all zero most of times, leading to wrong judge.

align_data = reader.read((16 - pre_align % 16) % 16)
    if any(align_data):
        reader.Position = pre_align
    else:
        self._uses_block_alignment = True

i tested serveral unity 2019.4.x bundle, for 2019.4.15 and higher, header.version should be 7 and with align
data.unity3d.zip(2019.4.14 and 2019.4.15)

[K0lb3]

Thanks for investigating and fixing this.
I'm a bit surprised about the empty hashes, but somehow it's also not exactly surprising -.-'