Fixed: a bug for range generatoion during week-end

The range generator failed during week-end, because no range is selected (lastStart and endDate is null).

with this commit, the rangeGenerator may return null instead of an array, which means no sms will be send.

src/Bundle/ChillCalendarBundle/Service/ShortMessageNotification/CalendarForShortMessageProvider.php

@@ -51,8 +51,13 @@ class CalendarForShortMessageProvider
      */
     public function getCalendars(DateTimeImmutable $at): iterable
     {
-        ['startDate' => $startDate, 'endDate' => $endDate] = $this->rangeGenerator
-            ->generateRange($at);
+        $range = $this->rangeGenerator->generateRange($at);
+
+        if (null === $range) {
+            return;
+        }
+
+        ['startDate' => $startDate, 'endDate' => $endDate] = $range;
 
         $offset = 0;
         $batchSize = 10;