const QPixmap should perform as fast as a pointer
there is a replacement version for Qt5 but it requires Qt5.15, so we are using indirection witch is unsafer but it should be ok as all the action is happen in the main thread
When an issues is open from YACReaderLibrary we can check if it is a manga an update the UI to enable manga reading.
This also fixes going previous/next from the ui/shortcuts
closeEvent is accepted by default, so this commit does not change the
application behavior. But Qt documentation recommends not relying on the
default value as subclasses may choose to clear it in their constructor.
