Evaluator.IncrementDate(): Allow incrementing by 0 to simplify callin…

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Ical.Net/Evaluation/Evaluator.cs

@@ -55,11 +55,8 @@ protected IDateTime ConvertToIDateTime(DateTime dt, IDateTime referenceDate)
 
     protected void IncrementDate(ref DateTime dt, RecurrencePattern pattern, int interval)
     {
-        // FIXME: use a more specific exception.
         if (interval == 0)
-        {
-            throw new Exception("Cannot evaluate with an interval of zero.  Please use an interval other than zero.");
-        }
+            return;
 
         var old = dt;
         switch (pattern.Frequency)