Fix Debian postinst when there's no existing executable.
Fix Debian postinst when there's no existing executable.

greeca0204/heroku,vcgato29/heroku,vcgato29/heroku,duypq94/heroku,macedo/heroku,heroku/heroku,gregburek/heroku,greeca0204/heroku,sancopanco/heroku,dickeyxxx/heroku,heroku/heroku,macedo/heroku,heroku/heroku,dickeyxxx/heroku,duypq94/heroku,rkh/heroku,Faisalawanisee/heroku,rkh/heroku,uhoh-itsmaciek/heroku,sancopanco/heroku,macedo/heroku,greeca0204/heroku,Faisalawanisee/heroku,dickeyxxx/heroku,duypq94/heroku,rkh/heroku,gregburek/heroku,sancopanco/heroku,uhoh-itsmaciek/heroku,vcgato29/heroku,gregburek/heroku,Faisalawanisee/heroku