[LyX/master] Fix compilation with clang++ 3.6.2.

[Jean-Marc Lasgouttes]

commit cb8c52bd0c733b0df810ff91eaa5a73b4a594dc5
Author: Jean-Marc Lasgouttes <lasgout...@lyx.org>
Date:   Mon Nov 2 16:13:38 2015 +0100

    Fix compilation with clang++ 3.6.2.

diff --git a/src/Buffer.cpp b/src/Buffer.cpp
index e6096af..60a36b3 100644
--- a/src/Buffer.cpp
+++ b/src/Buffer.cpp
@@ -3435,7 +3435,7 @@ Buffer::References & Buffer::getReferenceCache(docstring 
const & label)
                return it->second.second;
 
        static InsetLabel const * dummy_il = 0;
-       static References const dummy_refs;
+       static References const dummy_refs = References();
        it = d->ref_cache_.insert(
                make_pair(label, make_pair(dummy_il, dummy_refs))).first;
        return it->second.second;