shell32: Implement IEnumShellItems for IShellItemArray.

[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://testbot.winehq.org/JobDetails.pl?Key=8193

Your paranoid android.


=== w7u (32 bit shlfolder) ===
shlfolder.c:3688: Test failed: Got 00000000

=== w8 (32 bit shlfolder) ===
shlfolder.c:3688: Test failed: Got 00000000