Bug 10267: Display the message only if the user enters too many characters

Bug 10267: Display the message only if the user enters too many characters

It seems better to display the warning if the user tries to enter too
many characters in the input.

Test plan:
With max=16
1. Copy/paste a string with 15, 16 and 17 characters
2. Enter a cardnumber of 15, 16, 17 characters
The warning should be displayed only the input overflows

Signed-off-by: Aleisha Amohia <aleishaamohia@hotmail.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>