2.19.x: The year setter changes the date to the last day of the month when overwriting a leap year

[mbeets-afro]

Description of the Issue
In version v2.19.0 and v2.19.1 if the date is in a leap year and you use the year setter to set the year to that same leap year again, the date portion is changed to the maximum date for that month.

ie if the date is 2016-01-05 and you set the year to 2016 again, the date changes to 2016-01-31

You'd expect the date to remain the same.

This does not occur in v2.18.1

perhaps related to (from the changelog):
#4199 [bugfix] Fix year setter on leap years, fixes #4024

Steps to Reproduce:
install moment in local folder:
npm install moment@2.19.0 --save

contents of test.js file:

const moment = require('moment');

const anotherMoment = moment('05 Jan 2017', 'DD MMM YYYY');
console.log(`${anotherMoment.format('YYYY-MM-DD')}`);
// outputs 2017-01-05

// Set the year to 2017 again
anotherMoment.year(2017);
console.log(`${anotherMoment.format('YYYY-MM-DD')}`);
// outputs 2017-01-05 -- no change as expected

// set year to a leap year
anotherMoment.year(2016);
console.log(`${anotherMoment.format('YYYY-MM-DD')}`);
// outputs 2016-01-05 -- year changes as expected

// set to the same leap year again
anotherMoment.year(2016);
console.log(`${anotherMoment.format('YYYY-MM-DD')}`);
// outputs 2016-01-31 -- date has changed!

Environment:
OS: Microsoft Windows 10 Pro
Version: 10.0.15063 Build 15063
Running in powershell as node test.js
Node: v6.11.1

Other information that may be helpful:

• The time zone setting of the machine the code is running on
  (UTC +02:00) Harare, Pretoria

• The time and date at which the code was run
  Fri Oct 20 2017 12:31:13 GMT+0200 (South Africa Standard Time)

• Other libraries in use (TypeScript, Immutable.js, etc)
  None

If you are reporting an issue, please run the following code in the environment you are using and include the output:
console.log( (new Date()).toString())
Fri Oct 20 2017 12:31:13 GMT+0200 (South Africa Standard Time)

console.log((new Date()).toLocaleString())
10/20/2017, 12:31:13 PM

console.log( (new Date()).getTimezoneOffset())
-120

console.log( navigator.userAgent)
// not running in the browser

console.log(moment.version)
2.19.0

[mattjohnsonpint]

Dup #4024 and fix pending in #4255.