bug#32012: 27.0.50; jit-lock--run-functions broken

["Andreas Röhler" <andreas.roehler@online.de>]

Running into it from ert-tests which call ‘jit-lock-fontify-now’

When reproduced from emacs -Q in scratch-buffer:

Debugger entered--Lisp error: (wrong-number-of-arguments (2 . 2) 0)
   jit-lock--run-functions()
   eval((jit-lock--run-functions) nil)
   elisp--eval-last-sexp(nil)
   eval-last-sexp(nil)
   funcall-interactively(eval-last-sexp nil)
   call-interactively(eval-last-sexp nil nil)
   command-execute(eval-last-sexp)

AFAIU caused by

jit-lock--run-functions from jit-lock.el, line 378, last line below

           (setq loose-beg (min loose-beg this-beg))
           (setq loose-end (max loose-end this-end))
           nil)))
     `(,(min tight-beg beg) ,(max tight-end end) ,loose-beg ,loose-end)))

‘min’ fails as ‘tight-beg’ is still nil, not updated from setq inside
pcase above.

GNU Emacs 27.0.50 (build 1, i686-pc-linux-gnu, GTK+ Version 3.14.5) of
  2018-05-29