[LyX/master] GuiSymbols: handle the case of an invalid data

[Guillaume Munch]

commit 03a0e983bc3d926d80c279e1c63ff401487e0062
Author: Guillaume Munch <g...@lyx.org>
Date:   Sat Dec 3 23:35:14 2016 +0100

    GuiSymbols: handle the case of an invalid data
    
    The docs do not guarantee that the index must be valid
---
 src/frontends/qt4/GuiSymbols.cpp |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/src/frontends/qt4/GuiSymbols.cpp b/src/frontends/qt4/GuiSymbols.cpp
index a08d7e5..2aadfff 100644
--- a/src/frontends/qt4/GuiSymbols.cpp
+++ b/src/frontends/qt4/GuiSymbols.cpp
@@ -218,6 +218,9 @@ public:
 
        QVariant data(QModelIndex const & index, int role) const
        {
+               if (!index.isValid())
+                       return QVariant();
+
                static QString const strCharacter = qt_("Character: ");
                static QString const strCodePoint = qt_("Code Point: ");