Debug button broken on master

*Created by: sampottinger*

For some reason debug button is broken on master but was working on #74 prior to re-merging master (@benfry - https://github.com/processing/processing4/commit/200afc4fd85ccfacd3a178174c4f3462095b8061). I remember fixing this when I first started #74. I'll see if I can find it again.