redirect on error, closes #1773

Closes #1773

Merge request studip/studip!1252

app/controllers/resources/export.php

@@ -273,12 +273,14 @@ class Resources_ExportController extends AuthenticatedController
             PageLayout::postError(
                 _('Der Startzeitpunkt darf nicht hinter dem Endzeitpunkt liegen!')
             );
+            $this->redirect(Request::get('from'));
             return;
         }
         if (!$this->weekdays) {
             PageLayout::postError(
                 _('Bitte mindestens einen Wochentag auswählen.')
             );
+            $this->redirect(Request::get('from'));
             return;
         }
 

app/views/resources/export/resource_bookings.php

 <? if ($resource): ?>
-    <form class="default" method="post"
-          action="<?= $controller->link_for('resources/export/bookings')?>">
+    <form class="default" method="post" action="<?= $controller->link_for('resources/export/bookings')?>">
+        <input type="hidden" name="from" value="<?= $controller->resource_bookings($resource->id)?>">
         <?= CSRFProtection::tokenTag() ?>
         <? if ($resource instanceof Room): ?>
             <input type="hidden" name="selected_rooms[]"

app/views/resources/resource/export_bookings.php

 <? if ($resource): ?>
-    <form class="default" method="post"
-          action="<?= $controller->link_for('resources/export/bookings')?>">
+    <form class="default" method="post" action="<?= $controller->link_for('resources/export/bookings')?>">
+        <input type="hidden" name="from" value="<?= $controller->export_bookings($resource->id)?>">
         <?= CSRFProtection::tokenTag() ?>
         <? if ($resource instanceof Room): ?>
             <input type="hidden" name="selected_rooms[]"