Even though that `view_building_coordinator::work_on_view_building` has
an `if` at the very beginning which checks whether the currently
processed base table is set, it only prints a message and continues
executing the rest of the function regardless of the result of the
check. However, some of the logic in the function assumes that the
currently processed base table field is set and tries to access the
value of the field. This can lead to the view building coordinator
accessing a disengaged optional, which is undefined behavior.
Fix the function by adding the clearly missing `co_await` to the check.
A regression test is added which checks that the view building state
observer - a different fiber which used to print a weird message due to
erroneus view building coordinator behavior - does not print a warning.
Fixes: scylladb/scylladb#27363Closesscylladb/scylladb#27373
(cherry picked from commit 654ac9099b)
Closesscylladb/scylladb#27406
e4b1c1f38b