dlls/opengl32/wgl.c: minor dealloc fix

[Stefan Dösinger]

Am 01.01.2007 um 11:03 schrieb Nick Burns:

> There can be a problem where the detach is hit before  
> internal_gl_extensions is allocated and it tries to free NULL and  
> dies...
>
> This just checks for the allocation before freeing -- very minor
>
> - Nick
HeapFree(GetProcessHeap(), 0, NULL) is supposed to be a nop, so the  
check is not needed.