DolphinQt2/NetPlay: Mark constructors explicit where applicable

Source/Core/DolphinQt2/NetPlay/NetPlayDialog.h

@@ -30,7 +30,7 @@ class NetPlayDialog : public QDialog, public NetPlayUI
 {
   Q_OBJECT
 public:
-  NetPlayDialog(QWidget* parent);
+  explicit NetPlayDialog(QWidget* parent);
   ~NetPlayDialog();
 
   void show(std::string nickname, bool use_traversal);