Fixed when property is not found.

Source/Core/Element.cpp

@@ -1577,7 +1577,7 @@ void Element::ProcessEvent(Event& event)
 			if (overflow_property == OVERFLOW_AUTO ||
 				overflow_property == OVERFLOW_SCROLL)
 			{
-				SetScrollTop(GetScrollTop() + wheel_delta * (GetFontFaceHandle() ? ElementUtilities::GetLineHeight(this) : GetProperty< int >(SCROLL_DEFAULT_STEP_SIZE)));
+				SetScrollTop(GetScrollTop() + wheel_delta * (GetFontFaceHandle() ? ElementUtilities::GetLineHeight(this) : (GetProperty(SCROLL_DEFAULT_STEP_SIZE) ? GetProperty< int >(SCROLL_DEFAULT_STEP_SIZE) : 0 )));
 				event.StopPropagation();
 			}
 		}