title: Flatpickr : set default date only if date value is null/empty
body: <p>I am using Flatpickr v4.6.3. Using following line of code to initialize it on text fields with class date.</p>
  
  <p>$( ".date" ).flatpickr({"dateFormat":"d-M-Y",disableMobile: "true","defaultDate":new Date()});</p>
  
  <p>Here, I want Flatpickr to show the date that is set in value of input field, and if textbox/input field value is not having a valid date the show default date.</p>
  
  <p>Problem : if I use defaultDate:new Date(), then it always overrides whatever date value is set on input field. Maybe I can write a method to invoke for defaultDate and parse input value myself and return accordingly. Please suggest.</p>