ut2004 makes a 2D window for the splash screen, which sets the screen
surface's pixels field. Then we tear down that video mode and create a GL
context, and the Quartz target isn't resetting the pixels field to NULL.

When you just create a GL window, the structure is memset'd to zero the
first time through, so unless you hit ut2004's codepath, you won't see the
bug.  :)

Without this patch, quitting a windowed ut2003/ut2004 game makes the OS dump a
warning about a bogus free() to stderr, but it doesn't actually crash. All we
need to do is explicitly initialize the current->pixels field.

--HG--
extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/trunk%40853