bug#19718: read_filtered_event echos mouse events until character is inputted

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Date: Tue, 25 Aug 2020 11:54:21 +0200
> Cc: 19718@debbugs.gnu.org
> 
> Yes, I've always wondered what the point of that was.  Test case:
> 
> M-: (read-char-exclusive "foo: ")
> <mouse-1>
> 
> After waiting a bit, the echo area will say:
> 
> I don't really see the point of that?  Are there any circumstances that
> this is useful?

Isn't this the normal Emacs echoing of prefix keys?  IOW, how is this
different from what you get if you type "C-x v" and wait for a bit?