[O] Bug: Multiple tag selection broken on maint

[Alex Branham]

I'm tracking maint. With the following file:

#+BEGIN_EXAMPLE
  #+TAGS: office(c) car(C)
  * one
#+END_EXAMPLE

Doing C-c C-q on the "one" heading will not let me set both office and
car tags. They are highlighted in the little selection popup, but only
the last one selected actually gets added.


Emacs  : GNU Emacs 26.0.91 (build 1, x86_64-pc-linux-gnu, X toolkit, Xaw3d 
scroll bars)
 of 2018-03-20
Package: Org mode version 9.1.7 (release_9.1.7-31-gb5a90a @ 
/home/alex/.emacs.d/lib/org/lisp/)