dns: prevent undefined values in results

When getaddrinfo linked-list results contain entries other than AF_INET
and AF_INET6, the resulting v8::Array will contain undefined values.
That's because initialization of v8::Array pre-allocates entries for all
linked-list nodes, but not all of them will be in the final results.
This commit ensures that the array only contains valid results.

PR-URL: https://github.com/nodejs/node/pull/3696
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

src/cares_wrap.cc

@@ -922,19 +922,12 @@ void AfterGetAddrInfo(uv_getaddrinfo_t* req, int status, struct addrinfo* res) {
     struct addrinfo *address;
     int n = 0;
 
-    // Count the number of responses.
-    for (address = res; address; address = address->ai_next) {
-      n++;
-    }
-
     // Create the response array.
-    Local<Array> results = Array::New(env->isolate(), n);
+    Local<Array> results = Array::New(env->isolate());
 
     char ip[INET6_ADDRSTRLEN];
     const char *addr;
 
-    n = 0;
-
     // Iterate over the IPv4 responses again this time creating javascript
     // strings for each IP and filling the results array.
     address = res;