This variable overrides history user data, which makes the current
article and position restoring code in ArticleView::loadFinished()
difficult to understand.
Encode the same logic in the history user data instead. This should make
the code more straightforward and less brittle in the face of changes.
MainWindow calls ArticleView::reload() when the group list is updated.
This updating may add/remove/reorder dictionaries in the active group.
MainWindow also calls ArticleView::reload() when the display or addon
style changes.
In both of the above scenarios uncontrolled jumps and current article
change can occur (see also the parent commit message).
Move setting articleToJump from above the only ArticleView's reload()
call into ArticleView::reload() itself.
When the first article in the list is current, expanding or collapsing
optional parts results in:
1) uncontrolled jumps due to the content height changes if the scroll
position is not (0, 0);
2) current article change if a non-first article is saved in history
user data (e.g. if a mouse click had made the first article active).
Treat the first current article in the same way as non-first ones.
This change also affects the case when the current article is not
present in the article list. If the current article is simply empty,
then there is no behavior change. If the current article is not empty,
it *must* be in the list, unless something else went wrong.
This way it is clearer that the pages history is updated just before
each navigation to a different page.
The call to ArticleView::saveHistoryUserData() now occurs slightly later
in ArticleView::showDefinition(). I don't think the intervening code can
affect the current article or window position. So the reordering most
likely does not affect application behavior.
Without the added saveHistoryUserData() call, returning back from the
enlarged picture page ("gdpicture") restores the current article and the
window position that were last saved. At this commit the "gdpicture"
behavior is consistent with regular links: returning back from the
enlarged picture page sets the article with the picture as current and
restores the window position at the time of the click on the picture.
