x11: fix out-of-bounds access in adopt_atoms() error handling

Two problems:

- `j` can be >= `SIZE`, and needs to be wrapped like in the rest of the
   code.

- `cookies[j % SIZE]` is not initialized if there's no atom in `from[j]`.

The is manifested when:

- We've already gone through one batch (>= 128 atoms) (in fact this
  cannot happen in call to `adopt_atoms` in the current code).

- An XCB request failed in the middle of a batch.

Signed-off-by: Ran Benita <ran234@gmail.com>