Disable MyGUI's scrollbar autorepeat (Fixes #2779)

We are currently using a custom implementation so as to support MyGUI version 3.2.1. When compiled with 3.2.2 or later, we need to disable MyGUI's autorepeat so that it doesn't interfere with ours.

apps/openmw/mwgui/widgets.cpp

@@ -539,6 +539,9 @@ namespace MWGui
             , mRepeatStepTime(0.1f)
             , mIsIncreasing(true)
         {
+#if MYGUI_VERSION >= MYGUI_DEFINE_VERSION(3,2,2)
+            ScrollBar::setRepeatEnabled(false);
+#endif
         }
 
         MWScrollBar::~MWScrollBar()