Cleanup overlay shaders when done (#10432)

Content.Client/CombatMode/ColoredScreenBorderOverlay.cs

@@ -25,6 +25,7 @@ namespace Content.Client.CombatMode
             worldHandle.UseShader(_shader);
             var viewport = args.WorldAABB;
             worldHandle.DrawRect(viewport, Color.White);
+            worldHandle.UseShader(null);
         }
     }
 }