[Fixed] Fails gracefully when no course modules are found.

[Fixed] Does not remove other modules from the activity link options due to same ids.

mod/lesson/mod.html

@@ -544,40 +544,43 @@
     <td>
     <?php
         // get the modules
-        $mods = get_course_mods($form->course);
-        $modinstances = array();
-        foreach ($mods as $mod) {
-            if ($mod->instance == $form->instance) {  // don't add this lesson
-                continue;
+        if ($mods = get_course_mods($form->course)) {
+            $modinstances = array();
+            foreach ($mods as $mod) {
+                if ($mod->instance == $form->instance and $mod->module == $form->module) {  // don't add this lesson
+                    continue;
+                }
+                // get the module name and then store it in a new array
+                if ($module = get_coursemodule_from_instance($mod->modname, $mod->instance, $form->course)) {
+                    $modinstances[$mod->modname][$module->id] = $module->name;
+                }
             }
-            // get the module name and then store it in a new array
-            if ($module = get_coursemodule_from_instance($mod->modname, $mod->instance, $form->course)) {
-                $modinstances[$mod->modname][$module->id] = $module->name;
+            ksort($modinstances); // sort by module name
+
+            // print out a select dropdown with optgroups
+            echo '<select id="menuactivitylink" name="activitylink">';
+            if ($form->activitylink == 0) {
+                echo '<option selected="selected" value="0">'.get_string('none')."</option>\n";
+            } else {
+                echo '<option value="0">'.get_string('none')."</option>\n";
             }
-        }
-        ksort($modinstances); // sort by module name
-
-        // print out a select dropdown with optgroups
-        echo '<select id="menuactivitylink" name="activitylink">';
-        if ($form->activitylink == 0) {
-            echo '<option selected="selected" value="0">'.get_string('none')."</option>\n";
-        } else {
-            echo '<option value="0">'.get_string('none')."</option>\n";
-        }
-        foreach ($modinstances as $module => $instances) {
-            echo '<optgroup label="'.get_string('modulename', $module).'">'."\n";
+            foreach ($modinstances as $module => $instances) {
+                echo '<optgroup label="'.get_string('modulename', $module).'">'."\n";
             
-            asort($instances);
-            foreach ($instances as $modid => $instance) {
-                if ($form->activitylink == $modid) {  // check for being selected
-                    echo '<option selected="selected" value="'.$modid.'">'.$instance."</option>\n";
-                } else {
-                    echo '<option value="'.$modid.'">'.$instance."</option>\n";
+                asort($instances);
+                foreach ($instances as $modid => $instance) {
+                    if ($form->activitylink == $modid) {  // check for being selected
+                        echo '<option selected="selected" value="'.$modid.'">'.$instance."</option>\n";
+                    } else {
+                        echo '<option value="'.$modid.'">'.$instance."</option>\n";
+                    }
                 }
+                echo "</optgroup>\n";
             }
-            echo "</optgroup>\n";
+            echo "</select>\n";
+        } else {
+            print_string('nocoursemods', 'lesson');
         }
-        echo "</select>\n";
         
         helpbutton("activitylink", get_string("activitylink", "lesson"), "lesson");
     ?>