directory_map() was skipping files and directories named "0"

Close #1757. Thanks @BennyC!
diff --git a/system/helpers/directory_helper.php b/system/helpers/directory_helper.php
index e7d3b5e..7d6b677 100644
--- a/system/helpers/directory_helper.php
+++ b/system/helpers/directory_helper.php
@@ -62,7 +62,7 @@
 			while (FALSE !== ($file = readdir($fp)))
 			{
 				// Remove '.', '..', and hidden files [optional]
-				if ( ! trim($file, '.') OR ($hidden === FALSE && $file[0] === '.'))
+				if ($file === '.' OR $file === '..' OR ($hidden === FALSE && $file[0] === '.'))
 				{
 					continue;
 				}