bug#56682: Fix the long lines font locking related slowdowns

[Gregory Heytings]

> > is apparently not enough, because "2-3" seems to install an 
> > integer-or-marker-p check on the third argument, which raises a 
> > (wrong-type-argument integer-or-marker-p nil) or (wrong-type-argument 
> > integer-or-marker-p t) error when narrow-to-region is called from 
> > byte-compiled code.
>
> Where's the integer-or-marker-p test installed and/or called from?

It is called when narrow-to-region, which has its own opcode, is called 
from byte-compiled code.  But I have no idea where it is installed.