wined3d: Don't emulate clipplanes with ffp vp and fix a wrong if condition.
b2f09fd20421d0a5e179b42332ca63bc5ac17d8a accidentally got the
device->vs_clipping check wrong. The FFP replacement should emulate
clipping if GL can't do this natively with vertex shaders, not the
other way. Also don't emulate clipping if we're using fixed function
vertex processing because (a) clipping is always supported by GL in
this case, and (b), fragment.texcoord[7] is undefined. (Or in the
worst case set to something bad by the app).