Summarized messages are not shown and cannot be selected. If
`opts.use_closest === false` and you try to select a summarized
message, we still have to use the closest instead of failing.
Eventually, we'll make summary rows selectable, but that would be
rather involved since selections are managed by ID, summaries exist only
in the DOM, and many parts of the code get the selection and expect
it to be a message.
(imported from commit 998c4f24aece84528cc9da53a47f9e4f5391702d)
eb2e8a15c3