lcl: do not try to open closed dataset in lookup controls since the moment of opening is unpredictable and can lead to crashes. See http://forum.lazarus.freepascal.org/index.php/topic,17355.msg96112.html

git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@43476 4005530d-fff6-0310-9dd1-cebe43e6787f
lcl: remove dbctrls.ExtractFieldName since it is not needed anymore (db.ExtractFieldName already implemented)

git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@43477 4005530d-fff6-0310-9dd1-cebe43e6787f