Flag featureless events

[JulienPeloton]

IMPORTANT: Please create an issue first before opening a Pull Request.
Linked to issue(s): Closes #363

What changes were proposed in this pull request?

Assign probability of -1.0 for events with null features. Only affects elasticc.

How was this patch tested?

CI

[codecov-commenter]

Codecov Report

Attention: 6 lines in your changes are missing coverage. Please review.

Comparison is base (2a21711) 56.40% compared to head (3ec6a75) 56.20%.

❗ Current head 3ec6a75 differs from pull request most recent head ffc93a3. Consider uploading reports for the commit ffc93a3 to get more accurate results

Files	Patch %	Lines
fink_science/random_forest_snia/processor.py	0.00%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #364      +/-   ##
==========================================
- Coverage   56.40%   56.20%   -0.21%     
==========================================
  Files          36       36              
  Lines        1631     1637       +6     
==========================================
  Hits          920      920              
- Misses        711      717       +6     

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