LCL: fixed OpenURL if URL is invalid, bug 24958

git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@42640 4005530d-fff6-0310-9dd1-cebe43e6787f
Debugger: fixed getting callstack (could go into an endless loop)

git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@42641 4005530d-fff6-0310-9dd1-cebe43e6787f