prevent php-warnings, closes #1789

app/controllers/course/admission.php

app/controllers/course/room_requests.php

app/controllers/questionnaire.php

app/views/course/timesrooms/editStack.php

app/views/questionnaire/_widget_questionnaire.php

app/views/questionnaire/overview.php

...s/questionnaire/question_types/freetext/freetext_edit.php

app/views/questionnaire/question_types/test/test_edit.php

lib/classes/Seminar.class.php

lib/evaluation/classes/Evaluation.class.php

lib/evaluation/classes/EvaluationAnswer.class.php

lib/evaluation/classes/EvaluationObject.class.php

lib/evaluation/classes/EvaluationTree.class.php

lib/evaluation/classes/EvaluationTreeEditView.class.php

lib/evaluation/classes/EvaluationTreeShowUser.class.php

lib/evaluation/classes/HTMLempty.class.php

lib/evaluation/evaluation.config.php

lib/evaluation/evaluation_admin_edit.inc.php

lib/evaluation/evaluation_admin_overview.lib.php

lib/evaluation/evaluation_admin_template.inc.php