[gnome-builder] editor-frame: fail fast on non-IdeBuffer

[Christian Hergert <chergert src gnome org>]

commit 46820960c8e59058960e250e949cb111db922e34
Author: Christian Hergert <christian hergert me>
Date:   Sun Sep 20 04:38:18 2015 -0700

    editor-frame: fail fast on non-IdeBuffer
    
    This should only happen during initiailization.

 src/editor/gb-editor-frame.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)
---
diff --git a/src/editor/gb-editor-frame.c b/src/editor/gb-editor-frame.c
index 067a039..ae1a3fc 100644
--- a/src/editor/gb-editor-frame.c
+++ b/src/editor/gb-editor-frame.c
@@ -62,6 +62,9 @@ gb_editor_frame_update_ruler (GbEditorFrame *self)
 
   buffer = gtk_text_view_get_buffer (GTK_TEXT_VIEW (self->source_view));
 
+  if (!IDE_IS_BUFFER (buffer))
+    return;
+
   /* update line/column text */
   if (self->show_ruler)
     {