sstable: fix use after free while applying extensions in sstable::open_file
sstable: fix use after free while applying extensions in sstable::open_file

sstable_file_io_extensions() return an array of pointers to extensions,
but do_for_each() may defer and the array will be destroyed. The match
keeps it alive until do_for_each completes.

Message-Id: <88a5aacb366e164dde1ba7a97a56eb68d3dbf955@scylladb.com>

avikivity/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla,avikivity/scylla,scylladb/scylla,avikivity/scylla