Fix the relative index used to make compressed SLCs

[scottstanie]

Discovered this after repeated batch runs of disp-s1, manually passing in stacks with compressed SLCs:

  File "/u/aurora-r0/staniewi/repos/dolphin/src/dolphin/workflows/wrapped_phase.py", line 171, in run
    ) = sequential.run_wrapped_phase_sequential(
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/u/aurora-r0/staniewi/repos/dolphin/src/dolphin/workflows/sequential.py", line 114, in run_wrapped_phase_sequential
    run_wrapped_phase_single(
  File "/u/aurora-r0/staniewi/repos/dolphin/src/dolphin/_decorators.py", line 106, in wrapper
    result = func(*args, **kwargs)
             ^^^^^^^^^^^^^^^^^^^^^
  File "/u/aurora-r0/staniewi/repos/dolphin/src/dolphin/workflows/single.py", line 239, in run_wrapped_phase_single
    cur_comp_slc = compress(
                   ^^^^^^^^^
  File "/u/aurora-r0/staniewi/repos/dolphin/src/dolphin/phase_link/_compress.py", line 39, in compress
    pl_referenced = pl_cpx_phase * pl_cpx_phase[reference_idx][None, :, :].conj()
                                   ~~~~~~~~~~~~^^^^^^^^^^^^^^^
IndexError: index 17 is out of bounds for axis 0 with size 15

The "extra_reference_index" asked for image index 17; there were 15 real, 5 compressed.

This fixes the phase_link.compress call to adjust for the real SLC offset.

Verified this worked by checking OPERA_CSLC * compressed_slc.conj() for the corresponding dates: