[Owncloud] Debugging a 500 return code.

[Peter Chubb]

Ha.  Finally fixed it.
This change allows zero-duration events and triggers to work.

diff --git a/3rdparty/Sabre/VObject/DateTimeParser.php b/3rdparty/Sabre/VObject/
DateTimeParser.php
index 1e2d54e..b615a0f 100644
--- a/3rdparty/Sabre/VObject/DateTimeParser.php
+++ b/3rdparty/Sabre/VObject/DateTimeParser.php
@@ -125,6 +125,10 @@ class Sabre_VObject_DateTimeParser {
 
             }
 
+           if ($duration == 'P') {
+                   $duration = 'PT0S';
+            }
+
             $iv = new DateInterval($duration);
             if ($invert) $iv->invert = true;