[LyX/master] Check the validity of an item before querying its tooltip

[Guillaume Munch]

commit 851ed60e49233f12138f2a8a5bc737dd8edc1b3d
Author: Guillaume Munch <g...@lyx.org>
Date:   Sat Dec 3 23:35:15 2016 +0100

    Check the validity of an item before querying its tooltip
    
    In case data() does not handle invalid items.
---
 src/frontends/qt4/ToolTipFormatter.cpp |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/src/frontends/qt4/ToolTipFormatter.cpp 
b/src/frontends/qt4/ToolTipFormatter.cpp
index d29012c..4594bbc 100644
--- a/src/frontends/qt4/ToolTipFormatter.cpp
+++ b/src/frontends/qt4/ToolTipFormatter.cpp
@@ -52,6 +52,8 @@ bool ToolTipFormatter::eventFilter(QObject * o, QEvent * e)
        // on the screen.
        QPoint pos = static_cast<QHelpEvent *>(e)->pos();
        QModelIndex item = iv->indexAt(pos);
+       if (!item.isValid())
+               return false;
        QVariant data = iv->model()->data(item, Qt::ToolTipRole);
        if (data.isValid() && data.typeName() == toqstr("QString"))
                // Unchanged if empty or already formatted