fix Call to a member function getStartWeeks() on null

plugin.manifest

 pluginname=CourseCopy
 pluginclassname=CourseCopy
-version=1.9.4
+version=1.9.5
 origin=data-quest
 studipMinVersion=4.0
 studipMaxVersion=5.3.99

views/copy/semester_start_und_ende.php

 <?php
+if ($semester) {
     $start_weeks = $semester->getStartWeeks();
     $last_week = count($start_weeks) - 1;
 ?>
@@ -29,3 +30,5 @@ $last_week = count($start_weeks) - 1;
         <? endforeach ?>
     </select>
 </label>
+<?php
+}