QFactoryLoader: Add namefilter for Windows.

No longer try to load all files in the directory as a plugin
which can cause problems when for example installers move
files around.

[ChangeLog][QtCore][QFactoryLoader][Windows] QFactoryLoader now
filters potential plugins by the ".dll" suffix.

Task-number: QTBUG-31476
Change-Id: Ia19d6211c72765aaba0a5d06e6d3b501e8a40fff
Reviewed-by: Lars Knoll <lars.knoll@theqtcompany.com>

src/corelib/plugin/qfactoryloader.cpp

@@ -120,7 +120,11 @@ void QFactoryLoader::update()
         if (!QDir(path).exists(QLatin1String(".")))
             continue;
 
-        QStringList plugins = QDir(path).entryList(QDir::Files);
+        QStringList plugins = QDir(path).entryList(
+#ifdef Q_OS_WIN
+                    QStringList(QStringLiteral("*.dll")),
+#endif
+                    QDir::Files);
         QLibraryPrivate *library = 0;
 
 #ifdef Q_OS_MAC