Bug 40516: Restore falsy boolean filter values

Test plan:
1) Navigate to ERM agreements and create an agreement
2) In the agreements table, click on the filter for Is Perpetual
3) Only the option for 'Yes' will be shown
4) Apply patch
5) yarn js:build
6) Hard refresh the browser and repeat step 2
7) Filter options for Yes and No should be available
8) Check the filtering works appropriately

Signed-off-by: Pedro Amorim <pedro.amorim@openfifth.co.uk>
Signed-off-by: Laura_Escamilla <laura.escamilla@bywatersolutions.com>
Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
(cherry picked from commit 5594945339)
Signed-off-by: Paul Derscheid <paul.derscheid@lmscloud.de>

koha-tmpl/intranet-tmpl/prog/js/datatables.js

@@ -1059,7 +1059,7 @@ function _dt_add_filters(table_node, table_dt, filters_options = {}) {
                 }
                 $(filters_options[i])
                     .filter(function () {
-                        return this._id && this._str;
+                        return this._id !== "" && this._str !== "";
                     })
                     .each(function () {
                         let optionValue =