Fix crash on editing.
Should not happen but happens on loading the doc attached to bug 274905, navigating the
textcursor to the end at the last page, pressing a few dozend times enter to add a new
page, add some text and scroll down.

[KCrash Handler]
6 0x00007f979def2ab5 in raise () from /lib64/libc.so.6
7 0x00007f979def3fb6 in abort () from /lib64/libc.so.6
8 0x00007f979ec50ef8 in qt_message_output (msgType=QtFatalMsg, buf=0x1a379a8 "ASSERT failure in QList<T>::operator[]: \"index out of range\", file /home/kde4/qt/include/QtCore/qlist.h, line 464") at /home/kde4/svn/qt/src/corelib/global/qglobal.cpp:2259
9 0x00007f979ec51074 in qt_message(QtMsgType, const char *, typedef __va_list_tag __va_list_tag *) (msgType=QtFatalMsg, msg=0x7f979edf9818 "ASSERT failure in %s: \"%s\", file %s, line %d", ap=0x7fffb9c7e9b0) at /home/kde4/svn/qt/src/corelib/global/qglobal.cpp:2305
10 0x00007f979ec518e2 in qFatal (msg=0x7f979edf9818 "ASSERT failure in %s: \"%s\", file %s, line %d") at /home/kde4/svn/qt/src/corelib/global/qglobal.cpp:2488
11 0x00007f979ec50aeb in qt_assert_x (where=0x7f979d432088 "QList<T>::operator[]", what=0x7f979d432075 "index out of range", file=0x7f979d432050 "/home/kde4/qt/include/QtCore/qlist.h", line=464) at /home/kde4/svn/qt/src/corelib/global/qglobal.cpp:2012
12 0x00007f979d40e241 in QList<QRectF>::operator[] (this=0x1837770, i=1) at /home/kde4/qt/include/QtCore/qlist.h:464
13 0x00007f979d4093a2 in KoTextLayoutArea::paint (this=0x1837690, painter=0x7fffb9c80690, context=...) at /home/snoopy/src/calligra/libs/textlayout/KoTextLayoutArea_paint.cpp:136
14 0x00007f978ae83678 in TextShape::paintComponent (this=0x10bf640, painter=..., converter=...) at /home/snoopy/src/calligra/plugins/textshape/TextShape.cpp:140
15 0x00007f97a3c6d517 in KoShapeContainer::paint (this=0x10bf640, painter=..., converter=...) at /home/snoopy/src/calligra/libs/flake/KoShapeContainer.cpp:157
16 0x00007f97a3c7293a in KoShapeManager::paintShape (this=0x14bf070, shape=0x10bf640, painter=..., converter=..., forPrint=false) at /home/snoopy/src/calligra/libs/flake/KoShapeManager.cpp:369
17 0x00007f97a3c70e27 in KoShapeManagerPaintingStrategy::paint (this=0x14bf5e0, shape=0x10bf640, painter=..., converter=..., forPrint=false) at /home/snoopy/src/calligra/libs/flake/KoShapeManagerPaintingStrategy.cpp:52
18 0x00007f97a3c726ba in KoShapeManager::paint (this=0x14bf070, painter=..., converter=..., forPrint=false) at /home/snoopy/src/calligra/libs/flake/KoShapeManager.cpp:335
19 0x00007f978f75b244 in KWCanvasBase::paint (this=0x14beb08, painter=..., paintRect=...) at /home/snoopy/src/calligra/words/part/KWCanvasBase.cpp:316
20 0x00007f978f7613c8 in KWCanvas::paintEvent (this=0x14beae0, ev=0x7fffb9c81160) at /home/snoopy/src/calligra/words/part/KWCanvas.cpp:156
21 0x00007f97a0169181 in QWidget::event (this=0x14beae0, event=0x7fffb9c81160) at /home/kde4/svn/qt/src/gui/kernel/qwidget.cpp:8346