Fix error that can occur when get_NAE_constraints is called for only fixing the axis

[dpanici]

No description provided.

[github-actions]

|             benchmark_name             |         dt(%)          |         dt(s)          |        t_new(s)        |        t_old(s)        | 
| -------------------------------------- | ---------------------- | ---------------------- | ---------------------- | ---------------------- |
 test_build_transform_fft_lowres         |     +0.42 +/- 5.03     | +2.23e-03 +/- 2.68e-02 |  5.35e-01 +/- 2.2e-02  |  5.33e-01 +/- 1.6e-02  |
 test_equilibrium_init_medres            |     -0.02 +/- 1.89     | -1.01e-03 +/- 7.98e-02 |  4.21e+00 +/- 5.4e-02  |  4.21e+00 +/- 5.9e-02  |
 test_equilibrium_init_highres           |     +0.40 +/- 1.41     | +2.20e-02 +/- 7.86e-02 |  5.59e+00 +/- 5.8e-02  |  5.56e+00 +/- 5.3e-02  |
 test_objective_compile_dshape_current   |     -0.12 +/- 6.24     | -4.87e-03 +/- 2.44e-01 |  3.90e+00 +/- 2.4e-01  |  3.91e+00 +/- 1.6e-02  |
 test_objective_compute_dshape_current   |     +1.48 +/- 2.11     | +5.39e-05 +/- 7.67e-05 |  3.69e-03 +/- 6.5e-05  |  3.64e-03 +/- 4.1e-05  |
 test_objective_jac_dshape_current       |     +2.27 +/- 7.91     | +9.26e-04 +/- 3.23e-03 |  4.17e-02 +/- 2.9e-03  |  4.08e-02 +/- 1.3e-03  |
 test_perturb_2                          |     -0.29 +/- 1.38     | -5.04e-02 +/- 2.43e-01 |  1.76e+01 +/- 6.7e-02  |  1.76e+01 +/- 2.3e-01  |
 test_proximal_freeb_jac                 |     +0.51 +/- 1.76     | +3.78e-02 +/- 1.32e-01 |  7.53e+00 +/- 1.1e-01  |  7.49e+00 +/- 7.6e-02  |
 test_solve_fixed_iter                   |     +0.46 +/- 59.74    | +2.30e-02 +/- 2.99e+00 |  5.03e+00 +/- 2.0e+00  |  5.00e+00 +/- 2.2e+00  |
 test_build_transform_fft_midres         |     -0.06 +/- 3.12     | -3.85e-04 +/- 1.89e-02 |  6.03e-01 +/- 1.8e-02  |  6.04e-01 +/- 5.7e-03  |
 test_build_transform_fft_highres        |     -0.44 +/- 1.38     | -4.37e-03 +/- 1.38e-02 |  9.96e-01 +/- 8.5e-03  |  1.00e+00 +/- 1.1e-02  |
 test_equilibrium_init_lowres            |     +2.03 +/- 3.53     | +7.64e-02 +/- 1.33e-01 |  3.84e+00 +/- 1.3e-01  |  3.76e+00 +/- 2.6e-02  |
 test_objective_compile_atf              |     +1.77 +/- 3.58     | +1.38e-01 +/- 2.79e-01 |  7.94e+00 +/- 1.9e-01  |  7.80e+00 +/- 2.1e-01  |
 test_objective_compute_atf              |     +1.36 +/- 4.21     | +1.43e-04 +/- 4.41e-04 |  1.06e-02 +/- 4.2e-04  |  1.05e-02 +/- 1.2e-04  |
 test_objective_jac_atf                  |     -1.83 +/- 2.83     | -3.72e-02 +/- 5.77e-02 |  2.00e+00 +/- 3.7e-02  |  2.04e+00 +/- 4.4e-02  |
 test_perturb_1                          |     -1.00 +/- 2.29     | -1.24e-01 +/- 2.84e-01 |  1.23e+01 +/- 2.1e-01  |  1.24e+01 +/- 1.9e-01  |
 test_proximal_jac_atf                   |     +0.17 +/- 0.66     | +1.39e-02 +/- 5.41e-02 |  8.21e+00 +/- 3.9e-02  |  8.20e+00 +/- 3.8e-02  |
 test_proximal_freeb_compute             |     -1.97 +/- 0.72     | -3.68e-03 +/- 1.34e-03 |  1.83e-01 +/- 7.0e-04  |  1.87e-01 +/- 1.1e-03  |

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.44%. Comparing base (1e4147d) to head (2b6fa66).
Report is 8 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1255   +/-   ##
=======================================
  Coverage   95.44%   95.44%           
=======================================
  Files          95       95           
  Lines       23423    23425    +2     
=======================================
+ Hits        22357    22359    +2     
  Misses       1066     1066           

Files with missing lines	Coverage Δ
desc/objectives/linear_objectives.py	97.05% <100.00%> (+<0.01%)	⬆️

... and 1 file with indirect coverage changes