System.NotSupportedException when zipping more than ~4.2 gb of data to a stream that doesn't support seeking #164

Steps to reproduce

You have to zip up enough data so that when the stream is writing the end of the central directory the function ZipHelperStream.WriteZip64EndOfCentralDirectory will be called. The first thing this does is call stream_.Position which immediately fails if the stream being written to doesn't support seeking and therefore doesn't support position. MSDN describes the relationship between the stream position property and the CanSeek property.

Expected behavior

Ideally, the stream's position would not be needed at all. Instead I think this should be tracked like the sizeEntries or startOfCentralDirectory is already being tracked by SharpZipLib.

Actual behavior

Since the underlying stream does not support seeking the stream's position property throws a System.NotSupportedException which then bubbles up.

Version of SharpZipLib

0.86.0.518

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