SynEdit: Ifdef Markup: fix several crashes

git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@41217 4005530d-fff6-0310-9dd1-cebe43e6787f
SynEdit: Ifdef Markup: force assert for testing

git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@41218 4005530d-fff6-0310-9dd1-cebe43e6787f