fix delay argument

src/index.php

@@ -107,6 +107,9 @@ catch (Exception $exception)
     );
 }
 
+// Default crawl delay in seconds
+$delay = 60;
+
 // Init optional commands
 if (isset($argv[1]))
 {
@@ -140,12 +143,18 @@ if (isset($argv[1]))
             );
 
         break;
+
+        default:
+
+            // Is valid crawl delay?
+            $seconds = (int) $argv[1];
+
+            if ($seconds > 1) {
+                $delay = $seconds;
+            }
     }
 }
 
-// Init crawl delay from argument or use default value
-$delay = empty($argv[0]) ? 60 : (int) $argv[0];
-
 // Begin crawler
 while (true)
 {