Fix broken page MiniBar
The MiniBar normally used to display page numbers and to provide
navigation buttons regressed since 01557c16 to only show an empty
non-functional button called "Page Number", along with multiple
warnings:
QObject::connect(MiniBar, QAction): invalid nullptr parameter
This is caused by moving setupViewerActions() to a place where
m_miniBar is not initialized yet, even though it has a runtime
connect-dependency on it.
By moving setupViewerActions() back, the MiniBar starts working
again. Now the m_addBookmark action, which is created in that
function, is not available anymore to be passed to the constructor of
BookmarkList. To avoid moving the setup of the latter away from the
rest of the sidebar code, only assigning the action to the bookmark
button contained in the BookmarkList is deferred to
setupViewerActions().
As requested, any accidental future nullptr-access will be handled by
crashing, even in Release builds, by omitting any checks.
Test Plan:
Page numbers show up again in toolbar, no more connect warnings.