fix: don't schedule job when havent the time

Signed-off-by: Vitor Mattos <1079143+vitormattos@users.noreply.github.com>

Author: vitormattos

lib/Service/ReminderService.php

@@ -118,6 +118,9 @@ protected function scheduleJob(string $startTime): ?DateTime {
 			Reminder::class,
 		);
 
+		if ($startTime === '') {
+			return null;
+		}
 		$runAfter = $this->getStartTime($startTime);
 		if (!$runAfter) {
 			return null;