Do not override grad_output at the end of arguments parsing

[foxtran]

Fixes #84

Now, it works as expected:

$ ./s-dftd3 CO.xyz --bj tpss --grad hdfgd
<...>
Virial:
--------------------------------------------------
      component           x          y          z
--------------------------------------------------
          x       0.000E+00  0.000E+00  0.000E+00
          y       0.000E+00  0.000E+00  0.000E+00
          z       0.000E+00  0.000E+00  1.711E-06
--------------------------------------------------

[Info] Dispersion energy written to .EDISP
[Info] Dispersion results written to 'hdfgd'

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 50.24%. Comparing base (3a50cbd) to head (29771d9). Report is 19 commits behind head on main.

Files with missing lines	Patch %	Lines
app/cli.f90	0.00%	0 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #85 +/- ## ========================================== + Coverage 48.63% 50.24% +1.60% ========================================== Files 34 24 -10 Lines 3707 2448 -1259 Branches 1518 987 -531 ========================================== - Hits 1803 1230 -573 + Misses 1207 877 -330 + Partials 697 341 -356 ```

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