[fpc-pascal] Last fix for RegExpr (error on empty input)

[Michael Van Canneyt]

On Sat, 15 Feb 2020, AlexeyT via fpc-pascal wrote:

> My app does mass replace with regex. in big text, user enters regex "\b" 
> and replaces it to eg "__". app calls Substitute() with each found 
> match, match is zero length so your code will NOT replace it to "__". 
> but it's needed to replace it to "__".

That can well be, but maybe in that case you need to change your app for
this particular use case. It's very much a corner case.

The alternative is to introduce a new boolean option for TRegexp which
controls the behaviour of substitute.

Since there are already 9 boolean properties, it may be better to introduce a Options
set property and mark the others deprecated.

Michael.