[client] egl: fix out by one error with letterbox rendering

This replaces the scaled `destRect` with a version that uses doubles
correcting the rounding error that is causing a failure to properly
clear the black bar areas.

client/renderers/EGL/egl.c

@@ -87,7 +87,7 @@ struct Inst
 
   int               width, height;
   float             uiScale;
-  LG_RendererRect   destRect;
+  struct DoubleRect destRect;
   LG_RendererRotate rotate; //client side rotation
 
   float translateX  , translateY;