Fix one of the tags/xref warnings in viper-ex.el

* lisp/emulation/viper-ex.el (ex-tag): Avoid a compilation warning
about find-tag-other-window.
1 job for master in 50 minutes and 39 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
failed #2221
test-all

00:50:39

 
Name Stage Failure
failed
test-all Test
make[2]: *** [check-doit] Error 1
Makefile:318: recipe for target 'check-doit' failed
make[2]: Leaving directory '/builds/emacs/emacs/test'
Makefile:293: recipe for target 'check-expensive' failed
make[1]: *** [check-expensive] Error 2
make[1]: Leaving directory '/builds/emacs/emacs/test'
Makefile:957: recipe for target 'check-expensive' failed
make: *** [check-expensive] Error 2
ERROR: Job failed: exit code 1