Swap order of read_objects and read_deltas in picca_xcf

[andreufont]

In the DR16 analysis we would first read the deltas, and used (zmin,zmax) from the deltas and (rpmax,rpmin) to set the relevant redshift range for quasars.

However, for some reason the current master branch has swapped these calls, and now we first read the objects.

Probably related to this, now the default values of z-min-obj and z-max-obj are set to (0, 10) while they were used to be None (to set them automatically based on zmin,zmax in deltas).

In the current branch, one keeps all quasars in the catalog, unless you specify by hand the redshift range. I would be in favour to going back to the previous setup.

@iprafols , @Waelthus, @alxogm - do you remember why this was changed?

[iprafols]

Nope, no idea when/why this was changed