Correct fix

Annoying, since this is not a checkbox, so we need to do extra work to
make sure we are doing a 0 <-> 1 conversion (since it is stored as a
string, not an integer, so it is a pain to flip the value since "0" is
not empty-ish in javascript).

Making the value -1 is not correct, since this is expected to be 0 or 1.

imp/js/compose-dimp.js

@@ -1273,7 +1273,7 @@ var DimpCompose = {
                 if (id.startsWith(pair.key + '_')) {
                     var t = pair.value.get(id.substring(pair.key.length + 1));
                     if (t) {
-                        $(t).setValue(1 - $F(t));
+                        $(t).setValue(~~(!(~~$F(t))));
                     }
                 }
             });