Qt: do not crash in TQtPage if parent is TTabControl


git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@42628 4005530d-fff6-0310-9dd1-cebe43e6787f
Qt: return clBackground as default color for TPanel. issue #24946


git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@42629 4005530d-fff6-0310-9dd1-cebe43e6787f