MB-11305 fix leak of config from handle_delete_bucket()

As identified by clang static analyser; ensure {config} is freed in
the case where (config[0] == 0) at line 2905.

Change-Id: Ic7a90434f57690371c6137b06ba0ff9a04f7809d
Reviewed-on: http://review.couchbase.org/37832
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>