Bugfix 2652 polar CF

[hsoh-u]

MET did not recognize the coordinate variable by using the standard name, "projection_x_coordinate" and "projection_y_coordinate". They are recognized as the coordinate variables

Changed literal 0 to nullptr (SonarQube code smell).

The fix for Bugfix: Refine support for coordinate dimensions in CF-compliant NetCDF files at main_V11.1 was applied to the develop branch (line 260 at nccf_file.cc)

Expected Differences

• Do these changes introduce new tools, command line arguments, or configuration file options? [No]
  
  If yes, please describe:
  

• Do these changes modify the structure of existing or add new output data types (e.g. statistic line types or NetCDF variables)? [No]
  
  If yes, please describe:
  

Pull Request Testing

• Describe testing already performed for these changes:
  

/d1/personal/hsoh/git/pull_request/MET_bugfix_2652_polar_CF/bin/plot_data_plane /d1/personal/hsoh/data/MET-2652/seaice_conc_monthly_sh_202208_f17_v04r00.nc nccf_polar_xy.ps 'name="cdr_seaice_conc_monthly"; level="(0,,)";' -v 4

DEBUG 4: Stereographic Grid Data:
DEBUG 4:   hemisphere: S
DEBUG 4:    scale_lat: -90
DEBUG 4:      lat_pin: -39.2753
DEBUG 4:      lon_pin: -137.767
DEBUG 4:        x_pin: 0
DEBUG 4:        y_pin: 0
DEBUG 4:   lon_orient: -180
DEBUG 4:         d_km: 25
DEBUG 4:        dy_km: -25
DEBUG 4:         r_km: 6371.2
DEBUG 4:           nx: 316
DEBUG 4:           ny: 332

• Recommend testing for the reviewer(s) to perform, including the location of input datasets, and any additional instructions:
  

N/A

• Do these changes include sufficient documentation updates, ensuring that no errors or warnings exist in the build of the documentation? [No]

• Do these changes include sufficient testing updates? [No]

• Will this PR result in changes to the test suite? [No]
  
  If yes, describe the new output and/or changes to the existing output:
  

• Please complete this pull request review by [Fill in date].
  

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[jprestop]

Thanks for testing, @hsoh-u, and for making these changes. I have reviewed the changes and ensured that all tests passed. Additionally, I changed the title to ensure the PR title matched the bugfix branch name. I approve this request.