kernel32/tests: GetPrivateProfileString tests should check if buffer terminates with null

[Christopher Smith]

Christopher Smith wrote:
> Our current tests for GetPrivateProfileString don't currently check to 
> make sure that our outbuffer is properly null terminated (and as it 
> turns out, in some cases it is not). The following patch adds a test 
> for that. It's "todo_wine"'d until my follow up patch is sent which 
> fixes the bug triggered by this change
I forgot to mention I tested this on Vista and it passes.

--Chris