Clipper: clear DisplayStart/DisplayEnd fields when Step() returns false.

imgui.cpp

@@ -3289,6 +3289,7 @@ void ImGuiListClipper::End()
         }
         TempData = NULL;
     }
+    DisplayStart = DisplayEnd = ItemsCount; // Clear this so code which may be reused past last Step() won't trip on a non-empty range.
     ItemsCount = -1;
 }