MDL-41634 - URL Download Repository doesn't warn when asked to download non-image files

repository/url/lang/en/repository_url.php

@@ -30,3 +30,4 @@ $string['url'] = 'URL';
 $string['url:view'] = 'Use URL downloader in file picker';
 $string['validname'] = 'You must provide a valid file name';
 $string['configplugin'] = 'URL repository type configuration';
+$string['validfiletype'] = 'You must provide a URL to an image file or a page containing images.';

repository/url/lib.php

@@ -168,6 +168,8 @@ EOD;
             } else if (strstr($info['content_type'], 'image/')) {
                 // download this file
                 $this->add_image_to_list($info['url'], $info['url'], $list);
+            } else {
+                $list['error'] = get_string('validfiletype', 'repository_url');
             }
 
             // parse all found css styles