fix crash when using ALDI usb-stick with broken filesystem

I was using a cheap usb-stick from ALDI supermarket with fat32,
and my application crashed because filesystem was empty.

Unrealistic scenario, but still just returning here false is better
than a crash

Change-Id: I8979d5a4e19ce57770ab03983e847b272ebf7019
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/io/qdiriterator.cpp

@@ -320,7 +320,8 @@ void QDirIteratorPrivate::checkAndPushDirectory(const QFileInfo &fileInfo)
 
 bool QDirIteratorPrivate::matchesFilters(const QString &fileName, const QFileInfo &fi) const
 {
-    Q_ASSERT(!fileName.isEmpty());
+    if (fileName.isEmpty())
+        return false;
 
     // filter . and ..?
     const int fileNameSize = fileName.size();