lib/vector/Vlib: Fix Resource Leak issue in open_nat.c (#5080)

Author: ShubhamDesai

lib/vector/Vlib/open_nat.c

@@ -53,8 +53,9 @@ int V1_open_old_nat(struct Map_info *Map, int update)
         Map->dig_fp.file = G_fopen_old(path, GV_COOR_ELEMENT, Map->mapset);
 
     if (Map->dig_fp.file == NULL) {
-        G_warning(_("Unable to open coor file for vector map <%s>"),
-                  Vect_get_full_name(Map));
+        const char *map_name = Vect_get_full_name(Map);
+        G_warning(_("Unable to open coor file for vector map <%s>"), map_name);
+        G_free((void *)map_name);
         return -1;
     }