Fix: Quote variable in integer comparison (HIGH priority)

HIGH PRIORITY FIXES:
- Line 994: Quote $result variable in [ ] test operator

Issue: Unquoted variables in test operators can cause issues if empty.
While $result from $? is always set, best practice is to quote all
variables in test operators for consistency.

RESULTS:
- 1 HIGH integer comparison issue fixed
- Better bash best practices followed

modules/performance/php-optimizer.sh

@@ -991,7 +991,7 @@ optimize_multiple_domains_wrapper() {
         optimize_domain_direct "$domain" "$username"
         local result=$?
 
-        if [ $result -eq 0 ]; then
+        if [ "$result" -eq 0 ]; then
             optimized=$((optimized + 1))
         else
             failed=$((failed + 1))