Fix get_intensity permissions

[will-moore]

See https://www.openmicroscopy.org/community/viewtopic.php?f=4&t=8698

To test:

• Choose another user's image in your non-default group and try to query pixel intensity.

[pwalczysko]

Tested on eel (could repeat two situations on outreach, user views data in their non-default group of other users, and admin views data in their non-default group of other users).
All works as expected now

Ready to merge FMPOV

[jburel]

@pwalczysko did you check with public user too?

[pwalczysko]

@jburel no, but tried this additional test just now: add public user to read-only-1, this is public user's non-default group. Then view image of another user as public user in read-only-1. All works fine.