view_update_generator: start: close staging_sstable_reader when done

The staging_sstable_reader has to be closed before it's destroyed.

Signed-off-by: Benny Halevy <bhalevy@scylladb.com>

db/view/view_update_generator.cc

@@ -96,6 +96,7 @@ future<> view_update_generator::start() {
 
                     inject_failure("view_update_generator_consume_staging_sstable");
                     auto result = staging_sstable_reader.consume_in_thread(view_updating_consumer(s, std::move(permit), *t, sstables, _as, staging_sstable_reader_handle), db::no_timeout);
+                    staging_sstable_reader.close().get();
                     if (result == stop_iteration::yes) {
                         break;
                     }