net: make isIP() return 0 on empty input

lib/net.js

@@ -1030,7 +1030,7 @@ Server.prototype.listenFD = function(fd, type) {
 //  and it does not detect more than one double : in a string.
 exports.isIP = function(input) {
   if (!input) {
-    return 4;
+    return 0;
   } else if (/^(\d?\d?\d)\.(\d?\d?\d)\.(\d?\d?\d)\.(\d?\d?\d)$/.test(input)) {
     var parts = input.split('.');
     for (var i = 0; i < parts.length; i++) {

test/simple/test-net-isip.js

@@ -36,12 +36,13 @@ assert.equal(net.isIP('::1'), 6);
 assert.equal(net.isIP('::'), 6);
 assert.equal(net.isIP('0000:0000:0000:0000:0000:0000:12345:0000'), 0);
 assert.equal(net.isIP('0'), 0);
+assert.equal(net.isIP(), 0);
+assert.equal(net.isIP(""), 0);
 
 assert.equal(net.isIPv4('127.0.0.1'), true);
 assert.equal(net.isIPv4('example.com'), false);
 assert.equal(net.isIPv4('2001:252:0:1::2008:6'), false);
 
 assert.equal(net.isIPv6('127.0.0.1'), false);
-assert.equal(net.isIPv4('example.com'), false);
+assert.equal(net.isIPv6('example.com'), false);
 assert.equal(net.isIPv6('2001:252:0:1::2008:6'), true);
-