Fix mark-defun when there's no spaces between successive defuns.

Fix mark-defun when there's no spaces between successive defuns.

The problem was a parse-partial-sexp call which tried to use the STOPBEFORE
argument to detect non-syntactic WS.  This fails on a "}", which does not
begin a sexp.

* lisp/emacs-lisp/lisp.h (beginning-of-defun--in-emptyish-line-p): Enhance to
handle BOL being in a string.
(beginning-of-defun-comments): Call the above function in place of the call
to parse-partial-sexp.