[Bug 56911] System.Windows.Forms: ContextMenuStrip -> SourceControl property is null

[WineHQ Bugzilla]

https://bugs.winehq.org/show_bug.cgi?id=56911

--- Comment #9 from Esme Povirk  ---
Possibly this should go in ToolStripMenuItem.OnClick, but we still need
ToolStripDropDown.Close to unset this in other cases. Checking reason seems
wrong. Application can detect whether Dismiss is called (by subclassing), so we
can't just go through an internal method instead.

Maybe some internal flag to delay this until ToolStripMenuItem.OnClick can
handle it after the Click handler? But that feels messy.