fix warnings for optional regexp blocks

helpers/SG_iCal_Duration.php

@@ -22,7 +22,7 @@ class SG_iCal_Duration {
 	public function __construct( $duration ) {
 		if( $duration{0} == 'P' || (($duration{0} == '+' || $duration{0} == '-') && $duration{1} == 'P') ) {
 			preg_match('/P((\d+)W)?((\d+)D)?(T)?((\d+)H)?((\d+)M)?((\d+)S)?/', $duration, $matches);
-			$results = array('weeks'=>(int)$matches[2],
+			$results = @ array('weeks'=>(int)$matches[2],
 							'days'=>(int)$matches[4],
 							'hours'=>(int)$matches[7],
 							'minutes'=>(int)$matches[9],