chart: Use enter instead of leave to update highlightitem
Users report segfaults when copying path and opening externally.
On mouse-downs and mouse-ups, leave_cb is called.
Sometimes it is called just after context_menu has closed,
thus setting highlighted_item to null.
The solution is to use the enter instead of the leave signal
to update highlighted_item.
Fixes
Fixes the issues on my machine, and both original reporters report the fix to work for them.
Edited by Yifan Zhu