ddraw: Stop crash when dd7 isnt installed

[Stefan Dösinger]

> Changelog:
> 	ddraw: Stop crash when dd7 isnt installed
Do you really think it is worth polluting the code for this case? I haven't
seen a windows box without dx7 since a LONG time. If you want to prevent a
crash I think it is better to add some santiy checks at the beginning of the
test and skip all the tests rather than polluting every test with lots and
lots of possible error conditions coming from old dx versions