Ceci-pressdown/pressup event listener adding bug fix.

Fixes a bug where we would add the 'on-ceci-pressdown/pressup' listeners every time 'attached' was fired (like after sorting a component in the designer) causing buttons to fire multiple "click" signals every time they were pressed.

Fixes #1917


indexOf(undefined) returns -1

It feels weird the way it's done, but it's safe and works.