libcurl: some OOM handling fixes

lib/slist.c

@@ -119,10 +119,7 @@ void curl_slist_free_all(struct curl_slist *list)
   item = list;
   do {
     next = item->next;
-
-    if(item->data) {
-      free(item->data);
-    }
+    Curl_safefree(item->data);
     free(item);
     item = next;
   } while(next);