Fixed incomplete decompression bug in System.IO.Compression.DeflateStream.

Call zlib's inflate() even if no data was read from the stream, there might still be some data left to process.

Originally reported by Eric Roller, as Xamarin bugzilla #17183.
https://bugzilla.xamarin.com/show_bug.cgi?id=17183

Reviewed by Rodrigo Kumpera.