Minor - fix PHP warnings

main/group/group_creation.php

@@ -28,8 +28,6 @@ if (isset($_POST['action'])) {
             if (isset($_POST['same_category']) && $_POST['same_category']) {
                 $useOnlyFirstCategory = true;
             }
-            $group1['category'] = isset($_POST['group_'.$i.'_category']) ? $_POST['group_'.$i.'_category'] : null;
-
             for ($i = 0; $i < $_POST['number_of_groups']; $i++) {
                 $group1['name'] = empty($_POST['group_'.$i.'_name']) ? get_lang('Group').' '.$i : $_POST['group_'.$i.'_name'];
                 $group1['category'] = isset($_POST['group_'.$i.'_category']) ? $_POST['group_'.$i.'_category'] : null;

main/group/settings.php

@@ -229,7 +229,7 @@ if ($form->validate()) {
         header('Location: group.php?'.api_get_cidreq(true, false));
     } else {
         Display::addFlash(Display::return_message(get_lang('GroupSettingsModified'), 'success'));
-        header('Location: group.php?'.api_get_cidreq(true, false).'&category='.$cat['id']);
+        header('Location: group.php?'.api_get_cidreq(true, false).'&category='.$categoryId);
     }
     exit;
 }