lib: Support `isset()' and `empty()' checks on CLI params

library/Icinga/Cli/Params.php

@@ -108,6 +108,18 @@ class Params
         return $this->standalone;
     }
 
+    /**
+     * Support isset() and empty() checks on options
+     *
+     * @param   $name
+     *
+     * @return  bool
+     */
+    public function __isset($name)
+    {
+        return isset($this->params[$name]);
+    }
+
     /**
      * @see Params::get()
      */