[ci skip] Normalize tabs/spaces

Partial changes from PR #4016
diff --git a/system/libraries/Upload.php b/system/libraries/Upload.php
index 20ddfc1..8a2dec7 100644
--- a/system/libraries/Upload.php
+++ b/system/libraries/Upload.php
@@ -1023,7 +1023,7 @@
 
 		if (count($x) === 1)
 		{
-		    return '';
+			return '';
 		}
 
 		$ext = ($this->file_ext_tolower) ? strtolower(end($x)) : end($x);