Fix false emailVerified on user model update

We noticed that every time the user model updates, the emailVerified
column would change to false, even though the email was not changed
at all.

I took a look and realized there might be an error in
https://github.com/strongloop/loopback/commit/eb640d8

The intent of the commit just mention is to make emailVerified false
when the email gets changed, but notice that ctx.data.email is null
on updates, so the condition is always met and emailVerified always
becomes false.

This commit fixes the issue just mentioned.

common/models/user.js

@@ -845,7 +845,7 @@ module.exports = function(User) {
         if (emailChanged && ctx.Model.settings.emailVerificationRequired) {
           ctx.instance.emailVerified = false;
         }
-      } else {
+      } else if (ctx.data.email) {
         emailChanged = ctx.hookState.originalUserData.some(function(data) {
           return data.email != ctx.data.email;
         });

test/user.test.js

@@ -2358,6 +2358,28 @@ describe('User', function() {
       ], done);
     });
 
+    it('should not set verification to false after something other than email is updated',
+      function(done) {
+        User.settings.emailVerificationRequired = true;
+        async.series([
+          function updateUser(next) {
+            userInstance.updateAttribute('realm', 'test', function(err, info) {
+              if (err) return next(err);
+              assert.equal(info.realm, 'test');
+              next();
+            });
+          },
+          function findUser(next) {
+            User.findById(userInstance.id, function(err, info) {
+              if (err) return next(err);
+              assert.equal(info.realm, 'test');
+              assert.equal(info.emailVerified, true);
+              next();
+            });
+          },
+        ], done);
+      });
+
     function createOriginalUser(done) {
       var userData = {
         email: 'original@example.com',