shlwapi: Test and fix the behaviour of the CopyTo method for file sizes not multiple of the internal buffer size, on SHC

[Marvin]

Hi,

While running your changed tests on Windows, I think I found new failures.
Being a bot and all I'm not very good at pattern recognition, so I might be
wrong, but could you please double-check?
Full results can be found at
https://newtestbot.winehq.org/JobDetails.pl?Key=3116

Your paranoid android.


=== wvista (32 bit istream) ===
istream.c:669: Test failed: SHCreateStreamOnFileEx failed with ret=0x8007007b

=== w2008s64 (64 bit istream) ===
istream.c:669: Test failed: SHCreateStreamOnFileEx failed with ret=0x8007007b