[gnome-builder] xml: fix assertion

[Christian Hergert <chergert src gnome org>]

commit 7d9dac28b066e2c67b9feee1ea1b9bc029ff6207
Author: Christian Hergert <christian hergert me>
Date:   Thu May 14 01:58:26 2015 -0700

    xml: fix assertion

 libide/xml/ide-xml-highlighter.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/libide/xml/ide-xml-highlighter.c b/libide/xml/ide-xml-highlighter.c
index f5e7694..0404d2f 100644
--- a/libide/xml/ide-xml-highlighter.c
+++ b/libide/xml/ide-xml-highlighter.c
@@ -145,7 +145,7 @@ ide_xml_highlighter_set_buffer (IdeXmlHighlighter *highlighter,
   IdeXmlHighlighter *self = (IdeXmlHighlighter *)highlighter;
 
   g_assert (IDE_IS_HIGHLIGHTER (self));
-  g_assert (IDE_IS_BUFFER (buffer));
+  g_assert (!buffer || IDE_IS_BUFFER (buffer));
 
   if (self->buffer != buffer)
     {