Decrementing year on month view doesn't display the correct year on the navigator

[YounesM]

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Plunkr Case (Bug Reports)
Please demonstrate your case at stackblitz by using the issue template below. Issues without a test case have much less possibility to be reviewd in detail and assisted.

Current behavior

Expected behavior

https://stackblitz.com/github/primefaces/primeng-issue-template

Current behavior
If years navigator is disabled, decrementing or incrementing year on month view doesn't display the correct year on the navigator.

Expected behavior
Navigating through year should display the correct year even without the year navigator

Minimal reproduction of the problem with instructions
Add a calendar without the year navigator

What is the motivation / use case for changing the behavior?
We're using primeng in many projects and we need a working month picker.

Please tell us about your environment:

• Angular version: 6.X

• PrimeNG version: 6.0.1

• Browser: all

• Language: TypeScript

• Node (for AoT issues): node --version = 8.11.3

[cyberrranger]

move my problem to #6114

[YounesM]

It's not the same problem, I updated the issue with the current / expected behavior