wined3d: Properly check for the front buffer in d3dfmt_get_conv().

dlls/wined3d/surface.c

@@ -1823,7 +1823,7 @@ static HRESULT d3dfmt_get_conv(const struct wined3d_surface *surface, BOOL need_
              * in which the main render target uses p8. Some games like GTA Vice City use P8 for texturing which
              * conflicts with this.
              */
-            if (!((blit_supported && device->fb.render_targets && surface == device->fb.render_targets[0]))
+            if (!((blit_supported && surface->swapchain && surface == surface->swapchain->front_buffer))
                     || colorkey_active || !use_texturing)
             {
                 format->glFormat = GL_RGBA;