fix fatal error on PHP 8

plugin.manifest

 pluginname=HISinOne
 pluginclassname=HISinOne
 origin=virtUOS
-version=0.3.9
+version=0.3.10
 studipMinVersion=4.2
-studipMaxVersion=5.0.99
+studipMaxVersion=5.4.99

views/show/index.php

@@ -23,7 +23,7 @@
             <select name="semester_id" style="width: auto;">
                 <? foreach (Semester::getAll() as $semester): ?>
                     <? if ($semester->ende > strtotime('-6 months')): ?>
-                        <option value="<?= $semester->id ?>" <?= method_exists($semester, 'isCurrent') ? $semester->isCurrent() : $semester->getcurrent() ? 'selected' : '' ?>>
+                        <option value="<?= $semester->id ?>" <?= $semester->current ? 'selected' : '' ?>>
                             <?= htmlReady($semester->name) ?>
                         </option>
                     <? endif ?>