swaync-service-dispatcher: simplify quoting

hosts/common/programs/swaynotificationcenter/swaync-service-dispatcher

@@ -17,7 +17,12 @@ log() {
 checkActive() {
   # simulate a dry-run start. if no actions would be performed, then the service is up.
   # alternative is s6-svstat, but that doesn't support oneshots
-  test -z "$(s6-rc -n 0 -b start "$service")" && echo true || echo false
+  local s6Output=$(s6-rc -n 0 -b start "$service")
+  if [ -z "$s6Output" ]; then
+    echo true
+  else
+    echo false
+  fi
 }
 startService() {
   log "startService: $service"