mscoree: Return S_OK if mono runtime is found

[Dan Kegel]

Hi Bryan,
I believe your patch lets me install WinBITS successfully.  Thanks!
- Dan

p.s. To be precise, it let
winetricks mono12
wine msiexec /i WinBITS.msi
work.  I then had to do
  winetricks gdiplus corefonts
else the startup would complain about a missing font.
Now mono's only complaining about
GetThreadContext failed in gc, but that's another kettle of fish.