Ensure the command exist before adding an alias
Ensure the command exist before adding an alias

Fixes #371

casimir/kakoune,alpha123/kakoune,alexherbo2/kakoune,casimir/kakoune,jkonecny12/kakoune,flavius/kakoune,ekie/kakoune,occivink/kakoune,zakgreant/kakoune,lenormf/kakoune,elegios/kakoune,mawww/kakoune,Asenar/kakoune,jkonecny12/kakoune,zakgreant/kakoune,jkonecny12/kakoune,zakgreant/kakoune,occivink/kakoune,mawww/kakoune,ekie/kakoune,elegios/kakoune,ekie/kakoune,jjthrash/kakoune,jkonecny12/kakoune,flavius/kakoune,danr/kakoune,Somasis/kakoune,lenormf/kakoune,jjthrash/kakoune,ekie/kakoune,alexherbo2/kakoune,danr/kakoune,Asenar/kakoune,zakgreant/kakoune,alpha123/kakoune,Asenar/kakoune,alexherbo2/kakoune,danr/kakoune,elegios/kakoune,jjthrash/kakoune,flavius/kakoune,mawww/kakoune,danr/kakoune,occivink/kakoune,elegios/kakoune,mawww/kakoune,Somasis/kakoune,Somasis/kakoune,casimir/kakoune,casimir/kakoune,alexherbo2/kakoune,alpha123/kakoune,lenormf/kakoune,lenormf/kakoune,Somasis/kakoune,jjthrash/kakoune,alpha123/kakoune,flavius/kakoune,Asenar/kakoune,occivink/kakoune