rados.cc: fix pool alignment check

Only check pool alignment if io_ctx is initialized.

Introduced in 304b08a23a3db57010078046955a786fe3589ef8
Fixes: #8652
Signed-off-by: Samuel Just <sam.just@inktank.com>

(cherry picked from commit d7350a3741bf4cdb270c6361e68090fe280cf36d)

Conflicts:
	src/tools/rados/rados.cc