[Patch, fortran] Fix PR19101 missing & in character continuation not caught

[Tobias Schlüter]

Quoting Jerry DeLisle <jvdelisle@verizon.net>:
> The attached patch fixes the bug.  I used gfc_fatal_error because the match
> routines backup a lot and you can get multiple error messages similar to the
> "tabs are evil" patch.

I'm not going to obstruct this patch beyond this mail, my contributions have
been too few lately that I would feel in a position to do so, but I'm strongly
opposed to issuing a fatal error for an error such a trivial error (and the
same goes for Steve's patch to kill tabs).  I'd even go so far as claiming that
issuing a fatal error would be worse than silently accepting the erroneous code,
as the error is really rather trivial.  Is there really no way of recovering
gracefully, say by simply skipping the rest of the line, issuing a gfc_error,
and calling reject_statement, or some permutation thereof?

Thanks for considering this,
- Tobi