dns: fix GetAddrInfo assert

The method GetAddrInfo() is used by more than just dns.lookup(), and in
those cases a third argument isn't passed. This caused the following
check to abort:

  assert(args[3]->IsInt32());

Fixes: 4306786 "net: don't prefer IPv4 addresses during resolution"

Signed-off-by: Trevor Norris <trev.norris@gmail.com>

lib/dns.js

@@ -102,17 +102,14 @@ function onlookup(err, addresses) {
 // lookup(hostname, [options,] callback)
 exports.lookup = function lookup(hostname, options, callback) {
   var hints = 0;
-  var family;
+  var family = 0;
 
   // Parse arguments
   if (typeof options === 'function') {
     callback = options;
     family = 0;
-  // Allow user to pass falsy values to options, and still pass callback.
   } else if (typeof callback !== 'function') {
     throw TypeError('invalid arguments: callback must be passed');
-  } else if (!options) {
-    family = 0;
   } else if (util.isObject(options)) {
     hints = options.hints >>> 0;
     family = options.family >>> 0;
@@ -123,8 +120,6 @@ exports.lookup = function lookup(hostname, options, callback) {
         hints !== (exports.ADDRCONFIG | exports.V4MAPPED)) {
       throw new TypeError('invalid argument: hints must use valid flags');
     }
-  } else {
-    family = options >>> 0;
   }
 
   if (family !== 0 && family !== 4 && family !== 6)

src/cares_wrap.cc

@@ -1014,12 +1014,11 @@ static void GetAddrInfo(const FunctionCallbackInfo<Value>& args) {
   assert(args[0]->IsObject());
   assert(args[1]->IsString());
   assert(args[2]->IsInt32());
-  assert(args[3]->IsInt32());
   Local<Object> req_wrap_obj = args[0].As<Object>();
   node::Utf8Value hostname(args[1]);
 
+  int32_t flags = (args[3]->IsInt32()) ? args[3]->Int32Value() : 0;
   int family;
-  int32_t flags = args[3]->Int32Value();
 
   switch (args[2]->Int32Value()) {
   case 0: