fix plot_3d trying to connect end surfaces for zeta not 2pi cases

[YigitElma]

For zeta not up to 2pi, the plot_3d will not try to connect end surfaces together. Works the same for the 2pi case. For the issue #717 .

[github-actions]

|             benchmark_name             |         dt(%)          |         dt(s)          |        t_new(s)        |        t_old(s)        | 
| -------------------------------------- | ---------------------- | ---------------------- | ---------------------- | ---------------------- |
 test_build_transform_fft_lowres         |     -3.12 +/- 1.38     | -6.16e-04 +/- 2.72e-04 |  1.91e-02 +/- 9.6e-05  |  1.97e-02 +/- 2.5e-04  |
 test_build_transform_fft_midres         |     -1.44 +/- 0.88     | -1.62e-03 +/- 9.93e-04 |  1.11e-01 +/- 5.9e-04  |  1.13e-01 +/- 8.0e-04  |
 test_build_transform_fft_highres        |     +0.94 +/- 0.60     | +4.79e-03 +/- 3.07e-03 |  5.17e-01 +/- 2.4e-03  |  5.12e-01 +/- 1.9e-03  |
 test_equilibrium_init_lowres            |     -0.87 +/- 1.86     | -3.94e-03 +/- 8.41e-03 |  4.48e-01 +/- 5.1e-03  |  4.52e-01 +/- 6.7e-03  |
 test_equilibrium_init_medres            |     -0.97 +/- 1.22     | -5.54e-03 +/- 7.00e-03 |  5.68e-01 +/- 3.2e-03  |  5.73e-01 +/- 6.2e-03  |
 test_equilibrium_init_highres           |     -0.16 +/- 1.37     | -1.58e-03 +/- 1.38e-02 |  1.00e+00 +/- 9.1e-03  |  1.01e+00 +/- 1.0e-02  |
 test_objective_compile_dshape_current   |     -0.47 +/- 4.86     | -2.53e-02 +/- 2.63e-01 |  5.38e+00 +/- 1.8e-01  |  5.41e+00 +/- 1.9e-01  |
 test_objective_compile_atf              |     +0.43 +/- 5.48     | +7.07e-02 +/- 9.06e-01 |  1.66e+01 +/- 7.3e-01  |  1.65e+01 +/- 5.4e-01  |
 test_objective_compute_dshape_current   |     -3.38 +/- 2.62     | -1.16e-04 +/- 9.02e-05 |  3.33e-03 +/- 5.8e-05  |  3.44e-03 +/- 6.9e-05  |
 test_objective_compute_atf              |     -2.09 +/- 2.30     | -2.41e-04 +/- 2.66e-04 |  1.13e-02 +/- 1.6e-04  |  1.15e-02 +/- 2.1e-04  |
 test_objective_jac_dshape_current       |     -3.60 +/- 9.49     | -5.06e-03 +/- 1.33e-02 |  1.35e-01 +/- 8.3e-03  |  1.40e-01 +/- 1.0e-02  |
 test_objective_jac_atf                  |     +1.09 +/- 3.08     | +8.67e-02 +/- 2.44e-01 |  8.01e+00 +/- 2.3e-01  |  7.92e+00 +/- 8.5e-02  |
 test_perturb_1                          |     -1.60 +/- 15.83    | -1.43e-01 +/- 1.41e+00 |  8.78e+00 +/- 1.0e+00  |  8.92e+00 +/- 9.6e-01  |
 test_perturb_2                          |     -2.67 +/- 6.43     | -4.53e-01 +/- 1.09e+00 |  1.65e+01 +/- 5.9e-01  |  1.70e+01 +/- 9.2e-01  |

[codecov]

Codecov Report

Merging #718 (4d200ce) into master (b0794c9) will increase coverage by 0.00%.
The diff coverage is 100.00%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #718   +/-   ##
=======================================
  Coverage   94.97%   94.97%           
=======================================
  Files          79       79           
  Lines       19322    19324    +2     
=======================================
+ Hits        18351    18353    +2     
  Misses        971      971           

Files	Coverage Δ
desc/plotting.py	89.03% <100.00%> (+0.01%)	⬆️