Input Mask sets DIRTY state incorrectly

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Current behavior
Clicking (focus) in the input mask and directly leaving it (blur) without typing any character sets the input state to DIRTY. That is incorrect and it not aligned with the Angular standard behavior. It also leads to a confusing visual user feedback.

Expected behavior
Only set DIRTY state if the user types anything (no matter if valid or invalid character).

• Angular version: 5.2.2

• PrimeNG version: 4.0.3