* now when rendering in page view mode, we only keep track of page
number instead of pos inside document. Because using pos inside
document for page view mode is really a bad idea and will lead to
many unsovlabe bugs...
After set font in ReaderFont:onReadSettings, we have to send UpdatePos
event in order to set m_is_rendered(member of LVDocView) to true.
Otherwise position inside document will be reset to 0 on first view
render, this makes the first page of document is always displayed on
document open.
So far, I don't know why this call will alter the value of m_is_rendered.
It just works...
