Vlib: fix G_zero() usage

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@59959 15284696-431f-4ddb-bdfa-cd5b030d7da7

lib/vector/Vlib/init_head.c

@@ -30,7 +30,7 @@ void Vect__init_head(struct Map_info *Map)
 {
     char buf[64];
 
-    G_zero(&(Map->head), sizeof(struct dig_head *));
+    G_zero(&(Map->head), sizeof(struct dig_head));
 
     /* organization */
     Vect_set_organization(Map, "");