CGuiWidgetDrawParms: Mark Default instance as const

This isn't ever modified, so it can be made const to prevent
unintentional modification (and allow it to be placed within the RO
segment).

Runtime/GuiSys/CGuiWidgetDrawParms.cpp

@@ -1,5 +1,5 @@
 #include "CGuiWidgetDrawParms.hpp"
 
 namespace urde {
-CGuiWidgetDrawParms CGuiWidgetDrawParms::Default = {};
+const CGuiWidgetDrawParms CGuiWidgetDrawParms::Default = {};
 }