Closes #2991.

Running the image extraction on an image with DeviceCMYK and JPXDecode
using a custom /Decode entry would previously fail when applying the LUT
to the image in `_apply_decode`. This was due to converting the image to
RGB, but the custom LUT having a size of 8 entries.

For my specific (non-disclosable) example everything works correctly
now, while all existing tests still pass. Honestly, I am not sure
whether all cases are handled correctly now, but at least the error is
gone ...

Malformed PDFs can contain circular /Prev references in the xref
chain (e.g., xref A -> /Prev -> xref B -> /Prev -> xref A).
This causes _read_xref_tables_and_trailers() to loop forever,
spamming "Overwriting cache for N M" warnings on every iteration
as the same objects are re-parsed and re-cached indefinitely.

Fix: Track visited xref offsets in a set. If a startxref value
has already been visited, log a warning and break the loop.

Closes #3654.

## What's new

### Security (SEC)
- Prevent infinite loop from circular xref /Prev references (#3655) by @rampageservices

### Bug Fixes (BUG)
- Fix wrong LUT size error (#3651) by @stefan6419846
- Fix handling of page boxes defined on `/Pages` (#3650) by @stefan6419846

[Full Changelog](6.7.1...6.7.2)