Add warning if add incorrect day or month values
When editing the book meta date of publication, if enter a number greater than 12 in the month spot it reverts to "12" and for month if bigger than 31 defaults to "31". Because the date is set to be dd-mm-yy; and DD-MM is not standard in US, this may happen often out of habit. It would be better if there was a clear warning rather than a default value added.