[LyX/master] Fix possible bug spotted by cppcheck

[Jean-Marc]

commit 1cdbb94ff53ba2e73d60aecd53c7b9b44b042701
Author: Jean-Marc <lasgout...@lyx.org>
Date:   Sat Jul 5 19:12:09 2014 +0200

    Fix possible bug spotted by cppcheck
    
    I am not sure what this locking is really about, but the new code seems to 
be the right thing to do.

diff --git a/src/mathed/MathMacro.cpp b/src/mathed/MathMacro.cpp
index f39112c..a6d92d9 100644
--- a/src/mathed/MathMacro.cpp
+++ b/src/mathed/MathMacro.cpp
@@ -332,7 +332,7 @@ void MathMacro::updateRepresentation(Cursor * cur, 
MacroContext const & mc,
        if (isUpdating_)
                return;
 
-       UpdateLocker(*this);
+       UpdateLocker locker(*this);
 
        // known macro?
        if (macro_ == 0)