MDL-50318 course: Fix the URL of embedded images at resources overview

Not only mod_resource instances are listed here. All modules that
declare their FEATURE_MOD_ARCHETYPE as MOD_ARCHETYPE_RESOURCE (well, all
but those without own view page, such as mod_label) are listed. So we
must use the real plugin name when rendering the intro field.

course/resources.php

@@ -134,7 +134,7 @@
     $icon = '<img src="'.$cm->get_icon_url().'" class="activityicon" alt="'.$cm->get_module_type_name().'" /> ';
 
     if (isset($resource->intro) && isset($resource->introformat)) {
-        $intro = format_module_intro('resource', $resource, $cm->id);
+        $intro = format_module_intro($cm->modname, $resource, $cm->id);
     } else {
         $intro = '';
     }