[libxml2] Fix a wrong return value in previous patch

[Daniel Veillard <veillard src gnome org>]

commit 2c437da7f09528002c4ae5ab57b7620ed43733f4
Author: Daniel Veillard <veillard redhat com>
Date:   Fri May 11 12:08:15 2012 +0800

    Fix a wrong return value in previous patch

 xmlreader.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/xmlreader.c b/xmlreader.c
index ef41927..c5ab60e 100644
--- a/xmlreader.c
+++ b/xmlreader.c
@@ -5625,7 +5625,7 @@ xmlReaderNewIO(xmlTextReaderPtr reader, xmlInputReadCallback ioread,
     if (input == NULL) {
         if (ioclose != NULL)
             ioclose(ioctx);
-        return (NULL);
+        return (-1);
     }
     return (xmlTextReaderSetup(reader, input, URL, encoding, options));
 }