Always fire join events for an rjoin (#651)

Always fire join events for an rjoin (#651)

Previously, there was an additional check
`if (!join_struct.wait_done)` at the beginning of an rjoin.

This usually had no effect as the join isn't usually done yet. But if
thread A is the first to enter the join and finishes before thread B
starts, then B will never enter the `if`.

The only effect this had was that B would not fire join events in these
rare cases. (After that we check `join_struct.wait_done` again anyway.)
As of this PR we will always fire the events, which makes them easier
to analyze consistently.

Before this PR, looking at the join events for a single thread would show
no traces of the rjoin happening, except for an extra restart event from
the other thread.