ole32/tests: Test for correct storage creation.

[Vincent Povirk]

You might just want to try reopening the file and checking its CLSID,
instead of directly checking the contents. That should make it more
obvious that something is seriously wrong. With the direct checks,
it's hard to figure out what the test actually means.

Anyway, this should be easy to fix. We just need to keep track of
whether the file has ever had a header, instead of assuming the header
is valid if the file is large enough to have one.