Fix crash when overwriting manually installed files

[HebaruSan]

Problem

If you try to overwrite a manually installed file with the current dev build, an unhandled exception is thrown:

Unhandled Exception: System.NotSupportedException: InflaterInputStream Length is not supported
   at ICSharpCode.SharpZipLib.Zip.Compression.Streams.InflaterInputStream.get_Length()
   at CKAN.ModuleInstaller.StreamsEqual(Stream s1, Stream s2)

Cause

icsharpcode/SharpZipLib#84 changed the zip lib to throw an exception if you ask it for the length of a file in a ZIP. Before that I think it would have returned the correct length, because ModuleInstaller.StreamsEqual correctly reported whether files were the same.

We upgraded to that version of the lib in #3329, so users are not yet affected by this.

Changes

Now ModuleInstaller.StreamsEqual compares its input streams without checking their lengths.

Fixes #3348.

[DasSkelett]

Smart compiler 😁

[HebaruSan]

Smart compiler

Heh, I thought about that, but a dumber compiler would complain about the function missing a return statement at the end.

[DasSkelett]

And works like a charm!
(Files modified at beginning, middle, and end, should've all edge cases covered :P)