Added a check for empty filename

No empty entries should be added to the completion list, but it seems
like this is what is happening. Maybe this warning will give some more
information about the problem.
Reviewed-by: Daniel Molkentin <daniel.molkentin@nokia.com>
(cherry picked from commit 5b6ccb04)

src/plugins/cpptools/cppmodelmanager.cpp

@@ -1120,6 +1120,10 @@ void CppModelManager::updateIncludesInPaths(QFutureInterface<void> &future,
             const QString suffix = fileInfo.suffix();
             if (suffix.isEmpty() || suffixes.contains(suffix)) {
                 QString text = fileName.mid(path.length() + 1);
+                if (text.isEmpty()) {
+                    qWarning() << Q_FUNC_INFO << "Empty filename?" << path << fileName;
+                    continue;
+                }
                 if (fileInfo.isDir()) {
                     text += QLatin1Char('/');