Fix: do not update a RV's Z-position when stationary while turning

When the direction of a RV changes the Z-position update logic was called,
which did nothing to the Z-position because that is only changed every other
step. By chance/luck this never triggered with RV's turning around, until
making the partial Z calculations consistent and moving the locations where
the Z-position is changed, causing the Z-position to be changed twice for
the RV that stayed at the same location.

src/roadveh_cmd.cpp

@@ -1473,7 +1473,7 @@ again:
 		 * A vehicle has to spend at least 9 frames on a tile, so the following articulated part can follow.
 		 * (The following part may only be one tile behind, and the front part is moved before the following ones.)
 		 * The short (inner) curve has 8 frames, this elongates it to 10. */
-		v->UpdateInclination(false, true);
+		v->UpdateViewport(true, true);
 		return true;
 	}