(sort-regexp-fields-next-record): New subroutine.

(sort-regexp-fields-next-record): New subroutine.
If the first search does not advance point and finds an empty match,
skip one char and search again.
(sort-regexp-fields): Use that subroutine.
Bind sort-regexp-fields-regexp, for sort-regexp-fields-next-record.
(sort-regexp-fields-regexp): Declared.
(sort-regexp-record-end): Declared.