Accept status in fits_get_colnum to continue search

[jishnub]

This matches the functionality provided by CFITSIO. A non-zero status does not necessarily indicate an error in this function, and the status may be used as an input to continue the search.

[codecov]

Codecov Report

Attention: Patch coverage is 16.66667% with 5 lines in your changes missing coverage. Please review.

Project coverage is 95.85%. Comparing base (4124926) to head (09ab8a1).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/CFITSIO.jl	16.66%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #89      +/-   ##
==========================================
- Coverage   96.17%   95.85%   -0.33%     
==========================================
  Files           1        1              
  Lines         890      893       +3     
==========================================
  Hits          856      856              
- Misses         34       37       +3     

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[jishnub]

Looks like FITSIO.jl explicitly expects this to error. Perhaps we need a new flag to preserve this behavior.