bug#40642: 27.0.90; htmlfontify's hfy-force-fontification misusing jit-lock-fontify-now

[Amin Bandali]

It seems that htmlfontify's `hfy-force-fontification' uses
`jit-lock-fontify-now' without first checking if `jit-lock' is activated
in the buffer.

Symptoms of this bug include errors like this:

jit-lock-fontify-now: Wrong type argument: number-or-marker-p, nil

The above is triggered when calling the scpaste-index command from a
recent version of scpaste [0] that uses the `htmlfontify-buffer'
function from htmlfontify when htmlize is not available [1].

[0]: https://github.com/technomancy/scpaste
[1]: https://github.com/technomancy/scpaste/commit/ca95a8d

Excerpt from *Backtrace*:

Debugger entered--Lisp error: (wrong-type-argument number-or-marker-p nil)
  jit-lock--run-functions(1 10813)
  jit-lock-fontify-now()
  hfy-force-fontification()
  htmlfontify-buffer()
  scpaste("index")
  scpaste-index()
  funcall-interactively(scpaste-index)
  call-interactively(scpaste-index record nil)
  command-execute(scpaste-index record)
  counsel-M-x-action("scpaste-index")

In GNU Emacs 27.0.90 (build 3, x86_64-pc-linux-gnu, X toolkit, Xaw3d scroll 
bars)
 of 2020-04-15 built on darrud
Repository revision: 485f24223fdca91d439b7beaaac33f66cb3bc2af
Repository branch: emacs-27
Windowing system distributor 'The X.Org Foundation', version 11.0.12004000
System Description: Debian GNU/Linux 10 (buster)