[FIX] portal: detect attachment selection even when same as previous

Before this commit selecting the same attachment was not detected, which
was a problem when the attachment had been mistakenly removed

After this commit when the same attachment is selected several times in
a row it still triggers the upload and gets attached

https://github.com/odoo/odoo/issues/42364

closes odoo/odoo#62278

X-original-commit: e9b1bca1d48afff8313d106266b02793cf77ab79
Signed-off-by: Jérémy Kersten (jke) <jke@openerp.com>

addons/portal/static/src/js/portal_composer.js

@@ -133,6 +133,8 @@ var PortalComposer = publicWidget.Widget.extend({
                 });
             });
         })).then(function () {
+            // ensures any selection triggers a change, even if the same files are selected again
+            self.$fileInput[0].value = null;
             self.$sendButton.prop('disabled', false);
         });
     },