Fix NULL check issues (5 HIGH issues resolved)

Added proper null/empty checks and variable quoting in 3 files:

1. wordpress-cron-manager.sh (2 issues):
   - Added validation for $site_path before use
   - Quoted variable in cron command to prevent word splitting
   - Lines 446-449: Check if path is empty or invalid before processing

2. malware-scanner.sh (1 issue):
   - Added safety check for $SCAN_DIR before suggesting rm -rf command
   - Prevents dangerous rm operations if variable is empty or root
   - Line 1583-1585: Guard against accidental deletions

3. mysql-restore-to-sql.sh (2 issues):
   - Quoted $datadir in echo statements showing manual commands
   - Lines 426, 441, 444, 447: Proper quoting in examples

Impact: Prevents potential issues from empty/undefined variables

modules/backup/mysql-restore-to-sql.sh

@@ -423,7 +423,7 @@ show_recovery_options() {
             done
             echo ""
             echo "    3. Fix ownership:"
-            echo "       chown mysql:mysql $datadir/$DATABASE_NAME/*.ibd"
+            echo "       chown mysql:mysql \"$datadir/$DATABASE_NAME\"/*.ibd"
         else
             echo "    1. Check error log manually:"
             echo "       grep -i 'cannot open\\|missing' $error_log"
@@ -438,13 +438,13 @@ show_recovery_options() {
         echo "    If you're missing many files, easier to restore all:"
         echo ""
         echo "    1. Remove partial database directory:"
-        echo "       rm -rf $datadir/$DATABASE_NAME"
+        echo "       rm -rf \"$datadir/$DATABASE_NAME\""
         echo ""
         echo "    2. Restore complete database directory from backup:"
-        echo "       cp -r /backup/path/$DATABASE_NAME $datadir/"
+        echo "       cp -r /backup/path/$DATABASE_NAME \"$datadir/\""
         echo ""
         echo "    3. Fix ownership:"
-        echo "       chown -R mysql:mysql $datadir/$DATABASE_NAME"
+        echo "       chown -R mysql:mysql \"$datadir/$DATABASE_NAME\""
         echo ""
         echo "    4. Re-run this script"
         echo ""