fix: prevent removing all listeners by checking them before unbinding

fix: prevent removing all listeners by checking them before unbinding

$(...).off(undefined) removes all the attached event listeners, including those outside Foundation of unrelated to the issue.

This commit fixes #11360 and probably others issues by checking for variables expected to be listeners names before using it to remove the listeners.

[This fix is compatible with v6.5]

Closes https://github.com/zurb/foundation-sites/issues/11360