[LyX/master] Check to make sure we have a preview loader.

[Richard Heck]

commit df022f91b4e8c4537f1d499c7ad6afce9fc9bad9
Author: Richard Heck <rgh...@lyx.org>
Date:   Sat Jun 11 23:03:15 2016 -0400

    Check to make sure we have a preview loader.
    
    Fixes coverity #23353.

diff --git a/src/insets/RenderPreview.cpp b/src/insets/RenderPreview.cpp
index b05dca6..59a870c 100644
--- a/src/insets/RenderPreview.cpp
+++ b/src/insets/RenderPreview.cpp
@@ -104,6 +104,9 @@ docstring const statusMessage(BufferView const * bv, string 
const & snippet)
 
        Buffer const & buffer = bv->buffer();
        graphics::PreviewLoader const * loader = buffer.loader();
+       // please coverity (probably worth the check anyway)
+       if (!loader)
+               return docstring();
        graphics::PreviewLoader::Status const status = loader->status(snippet);
 
        docstring message;