ares_data.c: iterate through substructs when freeing

Previous code recursed into substructures, which makes it more likely
that large/heavily-nested responses could use up lots of stack.

ares_data.c

@@ -40,10 +40,9 @@
 
 void ares_free_data(void *dataptr)
 {
+  while (dataptr != NULL) {
     struct ares_data *ptr;
-
+    void *next_data = NULL;
-  if (!dataptr)
-    return;
 
 #ifdef __INTEL_COMPILER
 #  pragma warning(push)
@@ -65,7 +64,7 @@ void ares_free_data(void *dataptr)
         case ARES_DATATYPE_MX_REPLY:
 
           if (ptr->data.mx_reply.next)
-          ares_free_data(ptr->data.mx_reply.next);
+            next_data = ptr->data.mx_reply.next;
           if (ptr->data.mx_reply.host)
             ares_free(ptr->data.mx_reply.host);
           break;
@@ -73,7 +72,7 @@ void ares_free_data(void *dataptr)
         case ARES_DATATYPE_SRV_REPLY:
 
           if (ptr->data.srv_reply.next)
-          ares_free_data(ptr->data.srv_reply.next);
+            next_data = ptr->data.srv_reply.next;
           if (ptr->data.srv_reply.host)
             ares_free(ptr->data.srv_reply.host);
           break;
@@ -82,7 +81,7 @@ void ares_free_data(void *dataptr)
         case ARES_DATATYPE_TXT_EXT:
 
           if (ptr->data.txt_reply.next)
-          ares_free_data(ptr->data.txt_reply.next);
+            next_data = ptr->data.txt_reply.next;
           if (ptr->data.txt_reply.txt)
             ares_free(ptr->data.txt_reply.txt);
           break;
@@ -90,19 +89,19 @@ void ares_free_data(void *dataptr)
         case ARES_DATATYPE_ADDR_NODE:
 
           if (ptr->data.addr_node.next)
-          ares_free_data(ptr->data.addr_node.next);
+            next_data = ptr->data.addr_node.next;
           break;
 
         case ARES_DATATYPE_ADDR_PORT_NODE:
 
           if (ptr->data.addr_port_node.next)
-          ares_free_data(ptr->data.addr_port_node.next);
+            next_data = ptr->data.addr_port_node.next;
           break;
 
         case ARES_DATATYPE_NAPTR_REPLY:
 
           if (ptr->data.naptr_reply.next)
-          ares_free_data(ptr->data.naptr_reply.next);
+            next_data = ptr->data.naptr_reply.next;
           if (ptr->data.naptr_reply.flags)
             ares_free(ptr->data.naptr_reply.flags);
           if (ptr->data.naptr_reply.service)
@@ -125,6 +124,8 @@ void ares_free_data(void *dataptr)
       }
 
     ares_free(ptr);
+    dataptr = next_data;
+  }
 }