title: primeNG calendar input invalid value
body: <p>when i key in an invalid value into the mode=range calendar inputbox
  <a href="https://i.stack.imgur.com/DiN3z.png" rel="nofollow noreferrer">enter image description here</a></p>
  <pre><code>&lt;p-calendar fxFlex=&quot;265px&quot; [showIcon]=&quot;true&quot; selectionMode=&quot;range&quot; inputId=&quot;range&quot; [dateFormat]=&quot;yy/MM/dd&quot;
              formControlName=&quot;glDate&quot; placeholder=&quot;yyyy/mm/dd - yyyy/mm/dd&quot;&gt;
          &lt;/p-calendar&gt;
  </code></pre>
  <p>can I verify the user input value?
  because, when I get this.formgroup.glDate.value, that always show 「null」unless I type correctly format (ex: 2022/01/01 - 2022/06/06), so what can I validate this field?</p>
  <p>User request :</p>
  <ol>
  <li>can manual entry range date, don't use readonlyInput = true.</li>
  <li>validation field input value, return error alert, or prohibit input invalid value.</li>
  </ol>