Do not overwrite the START_CRON variable if already exists

Author: sroze

php/shared/usr/local/share/env/40-stack

@@ -18,8 +18,10 @@ export APP_GROUP=${APP_GROUP:-www-data}
 export START_MODE=${START_MODE:-web}
 declare "START_MODE_${START_MODE^^}=true"
 
-START_CRON="$(convert_to_boolean_string "${START_MODE_CRON:-false}")"
-export START_CRON
+if [ ! -n "${START_CRON:-}" ]; then
+  START_CRON="$(convert_to_boolean_string "${START_MODE_CRON:-false}")"
+  export START_CRON
+fi
 
 APP_ENDPOINT_REWRITE="$(convert_to_boolean_string "${APP_ENDPOINT_REWRITE-true}")"
 export APP_ENDPOINT_REWRITE