backport fix crash: 1. m_blockRange is a smart-range that highlights the block for the given codefolding region 2. when the mouse is over the code folding border, m_blockRange is a valid smart range 3. F5 reloads the document, which deletes the smart range 4. now m_blockRange is a dangling pointer 5. moving the mouse deletes this dangling pointer -> crash

CCBUG: 160527

svn path=/branches/KDE/4.0/kdelibs/; revision=794895