RNA: Don't fill in color grid array when built without smoke

Array length is set to 0 in that case, so filling in first element is
likely to cause memory corruptions.

source/blender/makesrna/intern/rna_smoke.c

@@ -264,7 +264,6 @@ static void rna_SmokeModifier_color_grid_get(PointerRNA *ptr, float *values)
 	BLI_rw_mutex_unlock(sds->fluid_mutex);
 #else
 	(void)ptr;
-	memset(values, 0, 4 * sizeof(float));
 #endif
 }