check if document.hostname is empty before using it
check if document.hostname is empty before using it

can be empty in electron

fixes #277

thheller/shadow-devtools,thheller/shadow-cljs,thheller/shadow-cljs,thheller/shadow-devtools,thheller/shadow-devtools,thheller/shadow-devtools,thheller/shadow-cljs,thheller/shadow-cljs