Item240: minor whoopsie, can get an uninitialised var warning without…

… this

git-svn-id: http://svn.foswiki.org/trunk@849 0b4bb1d4-4e5a-0410-9cc4-b2b747904278

core/lib/Foswiki/Time.pm

@@ -409,7 +409,7 @@ sub parseInterval {
     }
 
     if (!defined($start)) {
-        $start = $end - _parseDuration( $first );
+        $start = ($end || 0) - _parseDuration( $first );
     }
     if (!defined($end)) {
         $end = $start + _parseDuration( $last );