Fix LZMA decompression

[0x07E5]

In Unity LZMA file, headers [5:13] is decompressed size, should be skipped.
This PR solves the decompression issue #237

[K0lb3]

You're right,
going by the lzma specs it should be [13:].

I guess that fixing this for good requires looking a bit into the lzma code of the python package.

[AXiX-official]

In LZMA1, headers [5:13] is decompressed size, that's right
but in unity, decompressed wouldnt be write into compressed data
witch means there‘s no need to skip and there was a slight problem with the previous lzma compress fixes

[K0lb3]

Hm, I guess one simply solution to the issue would be simply checking if 8:13 contains the decompressed length.
If it does, start at 13, if not, start at 8.
This would have to be stored somewhere for saving afterwards.

[AXiX-official]

Sorry I may not have a complete understanding of the problem before commenting
Did you encounter a file with decompressed length saved in the lzma data that failed to read?
My understanding of this part is basically from AssetStudio and AssetsTools.NET, at least for BundleFile, AssetsTools.NET encodes as LZMA1(in cpp use func lzma_alone_decoder) and indeed does not keep the decompressed length in the compressed data.
And the format of the lzma compressed ab file I exported using Unity is also like this
I don't know much about the rest, is there a sample file that causes the problem?