Small fixes

[kujaku11]

Made a few fixes to help the processing run to completion.

1. removing nan from window and setting nan values to mean of nanmean()
2. Try/except statement when validating decimation levels
3. Add logic if length of processing row is not 1

Take them as you like.

[codecov]

Codecov Report

Merging #291 (1f9af7c) into fourier_coefficients (d8b0c62) will decrease coverage by 0.08%.
The diff coverage is 65.11%.

@@                   Coverage Diff                    @@
##           fourier_coefficients     #291      +/-   ##
========================================================
- Coverage                 76.71%   76.64%   -0.08%     
========================================================
  Files                        86       86              
  Lines                      5463     5476      +13     
========================================================
+ Hits                       4191     4197       +6     
- Misses                     1272     1279       +7     

Files Changed	Coverage Δ
aurora/pipelines/time_series_helpers.py	73.79% <58.82%> (-0.66%)	⬇️
aurora/pipelines/transfer_function_kernel.py	88.83% <69.23%> (-1.72%)	⬇️

[kkappler]

thanks, these are helpful