Bug 36804: Fix clear filter

1) Visit serials and click "New subscription":
http://localhost:8081/cgi-bin/koha/serials/serials-home.pl
2) Enter '112' on the record input and '1' on the vendor input. Click "Next"
3) 'First issue publication date' -> Enter some date in the past
4) 'Frequency' -> Enter '2/day'
5) 'Subscription start date' Same as step 3)
6) 'Subscription end date' Some date in the future
7) 'Numbering pattern' -> Enter 'Number'
8) Click 'Test prediction pattern'. Click 'Save subscription'
9) On the left side menu -> Click "Serial collection". Click the yellow button 'Edit serials'
10) On the first serial, edit the status to 'Late'. Save.
11) Visit serials claims:
http://localhost:8081/cgi-bin/koha/serials/claims.pl?supplierid=1
12) Input some dates in "From" and "To"
13) Click 'Clear filter'. Notice it doesn't work.
14) Apply patch. Repeat.

Signed-off-by: David Nind <david@davidnind.com>

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>

koha-tmpl/intranet-tmpl/prog/en/modules/serials/claims.tt

@@ -288,7 +288,8 @@
             });
             $("#clearfilter").on("click",function(e){
                 e.preventDefault();
-                $("#from,#to").val("");
+                $("#from").flatpickr().clear();
+                $("#to").flatpickr().clear();
                 $("table#claimst tbody tr").show();
             });
             $("#claims_form").on("submit",function(){