Fix R&S ZNB setting npts in CW mode

[mgunyho]

Fixes #3151.

I branched off of v0.26, let me know if you want me to rebase onto master.

@jenshnielsen

[codecov]

Codecov Report

Merging #3168 (7c0ef60) into master (89f6020) will decrease coverage by 0.00%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master    #3168      +/-   ##
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- Coverage   65.91%   65.91%   -0.01%     
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  Files         217      217              
  Lines       28902    28903       +1     
==========================================
  Hits        19051    19051              
- Misses       9851     9852       +1     

[jenshnielsen]

@mgunyho Thanks, We can merge master into this branch and then merge so that should be fine. The fix looks good to me. Did you test it on a real instrument ?

[mgunyho]

Yeah I tested with an instrument. Setting npts() in the example I had in the issue works now. I also quickly skimmed through the driver if the current sweep type should be checked elsewhere, looks like this is the only place.