Fix dff calculation when passed a trace with all 'nan' values

[mikejhuang]

Some corrected_fluorescence traces are all invalidated traces that are all nan values.

If this is passed into compute_dff_trace, skip the dff computation and return the nan trace.

[codecov[bot]]

Codecov Report

Merging #561 (1368e0e) into main (09c00d5) will decrease coverage by 1.50%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #561      +/-   ##
==========================================
- Coverage   97.69%   96.20%   -1.50%     
==========================================
  Files         103      103              
  Lines        8130     7834     -296     
  Branches      767      767              
==========================================
- Hits         7943     7537     -406     
- Misses        109      219     +110     
  Partials       78       78              

Flag	Coverage Δ
event_detection_tests	?
general_tests	96.20% <100.00%> (-0.14%)	:arrow_down:

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
tests/utils/test_traces.py	100.00% <ø> (ø)
tests/modules/dff/test_dff.py	97.72% <100.00%> (+0.29%)	:arrow_up:

... and 81 files with indirect coverage changes