fixed change variable of project environment cause qtcreator crash

NameValueValidator use const reference save tooltip content which
created by temp variable tr() return.

Change-Id: Ie76b14108e02d74f5c1ca686b349ce948ef88c14
Reviewed-by: hjk <hjk@qt.io>
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

src/libs/utils/namevaluevalidator.h

@@ -49,7 +49,7 @@ public:
     void fixup(QString &input) const override;
 
 private:
-    const QString &m_toolTipText;
+    const QString m_toolTipText;
     Utils::NameValueModel *m_model;
     QTreeView *m_view;
     QModelIndex m_index;