FifoPlayer: Allow changing loop option at runtime

This option has always existed since it's used by FifoCI, but now it can be changed at runtime.  Looping is something that should almost always be on, but it can be useful to turn it off when frame-dumping is enabled so that hundreds of copies of the same frame aren't created.  Before, turning it off required restarting Dolphin.

Source/Core/DolphinQt/FIFO/FIFOPlayerWindow.h

@@ -65,6 +65,7 @@ private:
   QSpinBox* m_object_range_to;
   QLabel* m_object_range_to_label;
   ToolTipCheckBox* m_early_memory_updates;
+  ToolTipCheckBox* m_loop;
   QDialogButtonBox* m_button_box;
 
   QWidget* m_main_widget;