give user feedback for empty or invalid PDF exports

Collectors used to return an empty page list for a missing page, a missing
namespace or an empty selection, which then failed silently or crashed

give user feedback for empty or invalid PDF exports

Collectors used to return an empty page list for a missing page, a missing
namespace or an empty selection, which then failed silently or crashed when the
first page was accessed. They now throw a translated ExportException instead,
which the action handler turns into feedback: a flash message and redirect for
regular navigations, or an HTTP error with the message in the body for the
background download BookCreator uses. Dynamic message parts are HTML escaped
because that body is injected into the page via a jQuery html() sink.

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Added tests

These tests have been initially LLM written, I went through each of them
to make sure they make sense and fixed what I thought needed fixing.

However coverage is still not great and sho

Added tests

These tests have been initially LLM written, I went through each of them
to make sure they make sense and fixed what I thought needed fixing.

However coverage is still not great and should be improved in the
future.

show more ...