Check QFile::open() return value

Otherwise, QFile::readAll() will print annoying log messages about
failure. Can be avoided.

src/player/CodecsComponent.cpp

@@ -264,7 +264,8 @@ static bool useSystemVideoDecoders()
 static QString loadDeviceID(QString filename)
 {
   QFile path(filename);
-  path.open(QFile::ReadOnly);
+  if (!path.open(QFile::ReadOnly))
+    return "";
   auto res = QString::fromLatin1(path.readAll());
   if (res.size() < 32 || res.size() > 512)
     res = ""; // mark as invalid