Abort ajax call when the input is less than minimumInputLength

[mete89]

When using AJAX in combination with minimumInputLength in Select2, the existing request is not being aborted if the number of characters is reduced below the minimumInputLength.

Steps to reproduce:

Go to https://select2.org/data-sources/ajax
Open the first Select2 dropdown.
Enter a character and then immediately delete it.
Initially, you will see the message 'Please enter 1 or more characters', but shortly after, the results from the last AJAX call will appear.

Expected Result:
When the 'minimumInputLength' message is displayed, any ongoing AJAX call should be aborted. Furthermore, if the results from a previously initiated AJAX call are received, they should not override the 'minimumInputLength' warning.