#12373: Fix CanvasMode::drawSnapLine. It didnt know about the right page, just used the current page

git-svn-id: file:///svn/Scribus/trunk/Scribus@19546 11d20701-8431-0410-a711-e3c959e3b870
Add FPoint::isNull like QPoint has

git-svn-id: file:///svn/Scribus/trunk/Scribus@19547 11d20701-8431-0410-a711-e3c959e3b870
#8942: Fix dragging of guides

git-svn-id: file:///svn/Scribus/trunk/Scribus@19548 11d20701-8431-0410-a711-e3c959e3b870