os: fix crash in GetInterfaceAddresses

If uv_interface_addresses() returns UV_ENOSYS then interfaces and count
are uninitialised. This can cause a segmentation fault inside
GetInterfaceAddresses when it tries to use the invalid interfaces[].
Fix the issue by returning from GetInterfaceAddresses on the UV_ENOSYS
error.

This issue was observed when using uCLibc-ng version 1.0.9 because
uv_interface_addresses() in deps/uv/src/unix/linux-core.c incorrectly
undefines HAVE_IFADDRS_H.

Signed-off-by: Martin Bark <martin@barkynet.com>
PR-URL: https://github.com/nodejs/node/pull/4272
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Brian White <mscdex@mscdex.net>
Reviewed-By: Saúl Ibarra Corretgé <saghul@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Rod Vagg <rod@vagg.org>

src/node_os.cc

@@ -200,7 +200,7 @@ static void GetInterfaceAddresses(const FunctionCallbackInfo<Value>& args) {
   ret = Object::New(env->isolate());
 
   if (err == UV_ENOSYS) {
-    args.GetReturnValue().Set(ret);
+    return args.GetReturnValue().Set(ret);
   } else if (err) {
     return env->ThrowUVException(err, "uv_interface_addresses");
   }