Don't rewind the temporary stream on write to the main one (#104)

Context: dbe3236

dbe3236 fixed an issue of data corruption when deleting files from the
archive by properly creating temporary streams when `libzip` requested
data modifications.  However, a bug crept in which causes the temporary
stream to be rewound, instead of the destination one, when data is
written back.  This has the effect of overwriting the ZIP local file
header structure with, essentially, random data and causes errors
similar to:

    error XABBA7000: Xamarin.Tools.Zip.ZipException: Zip archive inconsistent: entry 0: invalid WinZip AES extra field
    Xamarin.Android.Common.targets(2289,2): error ANDZA0000: zip W 01-25 15:03:13  9516 56652 WARNING: header mismatch

The issue can be seen by either attempting to unpack the archive:

    $ 7z x base.zip
    ERROR: Headers Error : dex/classes.dex
    ERROR: Headers Error : root/assemblies/assemblies.blob

    $ unzip base.zip
    file #9:  bad zipfile offset (local header sig):  49783
    file #10:  bad zipfile offset (local header sig):  127988

Or by looking at the file with `zipinfo -vv base.zip`:

    Central directory entry #10:
    ---------------------------

      There are an extra 9 bytes preceding this file.

      root/assemblies/assemblies.blob

      offset of local header from start of archive:   127988 (000000000001F3F4h) bytes

Not only the local header is thought to be at the incorrect offset, it
also doesn't have the correct signature:

    # show valid header
    $ hexdump -n 4 -C base.zip
    00000000  50 4b 03 04                                       |PK..|

    # show invalid header
    $ hexdump -s 127988 -n 4 -C base.zip
    0001f3f4  49 be 37 16                                       |I.7.|

    $ hexdump -s $((127988 - 9)) -n 4 -C base.zip
    0001f3eb  88 26 de 2c                                       |.&.,|

Attempt to fix the problem by rewinding the destination stream on write.

Fix found by Dean Ellis (@dellis1972)

Author: grendello

LibZipSharp.props

@@ -1,6 +1,6 @@
 <Project DefaultTargets="Build" ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
   <PropertyGroup>
-    <_LibZipSharpAssemblyVersion>2.0.2</_LibZipSharpAssemblyVersion>
+    <_LibZipSharpAssemblyVersion>2.0.3</_LibZipSharpAssemblyVersion>
     <!--
       Nuget Version. You can append things like -alpha-1 etc to this value.
       But always leave the $(_LibZipSharpAssemblyVersion) value at the start.

LibZipSharp/Xamarin.Tools.Zip/ZipArchive.cs

@@ -808,7 +808,7 @@ internal static unsafe Int64 stream_callback (IntPtr state, IntPtr data, UInt64
 					if (offset < 0) {
 						return offset;
 					}
-					if (offset != stream.Seek (offset, SeekOrigin.Begin)) {
+					if (offset != destination.Seek (offset, SeekOrigin.Begin)) {
 						return -1;
 					}
 					break;