GoToFlow::setNumSlides() is called each time a comic is opened. So when
e.g. three comics were opened one after another without restarting
YACReader, each of the PictureFlow::centerIndexChanged* signals was
connected to GoToFlow::preload three times, which multiplied the number
of calls to preload() accordingly.
During my testing PictureFlow::centerIndexChanged* signals were never
emitted before the first call to GoToFlow::setNumSlides(), so connecting
in GoToFlow::GoToFlow() should not cause extra calls to preload().
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