Fix div-by-zero errors on files which don't have any changed content

[peppy]

There are cases where the length in write operations becomes zero, at which point this code will throw an exception and fail to create bsdiff deltas.

As this is critical to our production workflow, it has been temporarily published as ppy.Squirrel.windows (along with several other PRs that are not merged into official releases yet).

Test files which cause the issue to reproduce (large): https://www.dropbox.com/sh/p13oiqir02xzny1/AABUHNZeP2u2T-AjViFYCG6na?dl=0

[augustoproiete]

@peppy The test files are no longer available on your Dropbox. Would you be able to upload them somewhere else?

[peppy]

Sorry about that! I've restored the files, so the link should work again.

[adabru]

@peppy, does #1421 achieve the same thing?

[peppy]

I have no idea, but the test files are still available if you'd like to try.

We have long since given up hope and maintain our own fork.

[adabru]

Thanks for open sourcing and distributing your fork on nuget. I switched to your fork.

[MichaelBelousov]

looks related to #1784

[caesay]

This is the same problem that was fixed in #1421 and has already been merged to master. I don't know if this fix has been released on nuget, but this PR can be closed. It is also fixed in my fork which has superseded the ppy.Squirrel.windows package.