MDL-53351 lti: Do not throw PHP notice when deleting LTI instance

The typeid=0 is a valid and common value representing "Automatic, based
on launch URL" type. In that case, no record in the lti_types table is
found. Thence attempting to access its toolproxyid property used to
throw PHP notice.

mod/lti/lib.php

@@ -188,8 +188,10 @@ function lti_delete_instance($id) {
     lti_grade_item_delete($basiclti);
 
     $ltitype = $DB->get_record('lti_types', array('id' => $basiclti->typeid));
-    $DB->delete_records('lti_tool_settings',
-        array('toolproxyid' => $ltitype->toolproxyid, 'course' => $basiclti->course, 'coursemoduleid' => $id));
+    if ($ltitype) {
+        $DB->delete_records('lti_tool_settings',
+            array('toolproxyid' => $ltitype->toolproxyid, 'course' => $basiclti->course, 'coursemoduleid' => $id));
+    }
 
     return $DB->delete_records("lti", array("id" => $basiclti->id));
 }

mod/lti/tests/lib_test.php

@@ -0,0 +1,53 @@
+<?php
+// This file is part of Moodle - http://moodle.org/
+//
+// Moodle is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Moodle is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
+
+/**
+ * Provides {@link lti_lib_testcase} class.
+ *
+ * @package     mod_lti
+ * @category    test
+ * @copyright   2016 David Mudrak <[email protected]>
+ * @license     http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+
+defined('MOODLE_INTERNAL') || die();
+
+global $CFG;
+require_once($CFG->dirroot.'/mod/lti/lib.php');
+
+/**
+ * Unit tests for mod/lti/lib.php
+ *
+ * @copyright 2016 David Mudrak <[email protected]>
+ * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+class lti_lib_testcase extends advanced_testcase {
+
+    /**
+     * Test deleting LTI instance.
+     */
+    public function test_lti_delete_instance() {
+        $this->resetAfterTest();
+
+        $this->setAdminUser();
+        $course = $this->getDataGenerator()->create_course(array());
+        $lti = $this->getDataGenerator()->create_module('lti', array('course' => $course->id));
+        $cm = get_coursemodule_from_instance('lti', $lti->id);
+
+        // Must not throw notices.
+        course_delete_module($cm->id);
+    }
+}