[GRASS-dev] trunk r47474 breaks OGSF rendering of points on surface

[Maris Nartiss]

After r47474 in trunk OGSF incorrectly renders points on surface with
any symbol except X. Z values of points seem to be messed up.

Steps to reproduce:
1) nviz elev=elevation.dem point=bugsites
2) Visualize->Vector points->Icon type and change from sphere to X and back.

martinl, please fix this.

Also consider to add some more comments to gpd.c, as to casual reader
it reads like magic spell ;)

Maris.