fix pre-start script to check for directory before chown

Author: markdboyd

jobs/kibana-platform/templates/bin/pre-start.erb

@@ -5,4 +5,8 @@ if ! [[ $(ls -1 /var/vcap/packages/kibana-platform/plugins | wc -l) == 0 ]]; the
 fi
 
 cd /var/vcap/packages/kibana-platform
-chown -R vcap:vcap optimize config data plugins
+chown -R vcap:vcap config data plugins
+
+if [[ -d optimize ]]; then
+  chown -R vcap:vcap optimize
+fi