SwEditWin::MouseButtonDown: the selection of fields was messed up by a
call to rSh.SetCursor near the bottom of the method. This used to be
fixed up by SwEditWin::MouseButtonUp previously, but that was broken
with commit dcb08034.

To fix that move the field selection code to a place where it prevents
the other code from running, in the hope that it is not necessary.

Also it does not make any sense to select whole words when clicking on a
field, just selecting the field seems much better.

Change-Id: I8d604450789844b6a446cf3a35f62ed530d0328e
(cherry picked from commit 94721b2a)
Reviewed-on: https://gerrit.libreoffice.org/1925Reviewed-by: Miklos Vajna <vmiklos@suse.cz>
Tested-by: Miklos Vajna <vmiklos@suse.cz>