Remove input val when clearing Binary widget

On chromium the input does not trigger a change event if the value is the same
(the same file is selected twice).
So we force the null value when the widget is cleared.

issue8513
review265681003

src/view/form.js

@@ -3616,6 +3616,7 @@ function eval_pyson(value){
             }.bind(this));
         },
         clear: function() {
+            this.input_select.val(null);
             var filename_field = this.filename_field;
             if (filename_field) {
                 filename_field.set_client(this.record, null);