[ticket/13755] Ignore dots in path when determining file extension.

PHPBB3-13755

phpBB/includes/functions_upload.php

@@ -213,6 +213,8 @@ class filespec
 	*/
 	static public function get_extension($filename)
 	{
+		$filename = utf8_basename($filename);
+
 		if (strpos($filename, '.') === false)
 		{
 			return '';

tests/upload/filespec_test.php

@@ -213,6 +213,8 @@ class phpbb_filespec_test extends phpbb_test_case
 			array('file.phpbb.gif', 'gif'),
 			array('file..', ''),
 			array('.file..jpg.webp', 'webp'),
+			array('/test.com/file', ''),
+			array('/test.com/file.gif', 'gif'),
 		);
 	}