Default rsets assigned to -1

[shuds13]

rsets["assigned"] must to default to -1, not zero, now we can assign resources to worker 0.

[codecov]

Codecov Report

Attention: Patch coverage is 80.00000% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 86.87%. Comparing base (0d99592) to head (7001440).
Report is 46 commits behind head on develop.

Files	Patch %	Lines
libensemble/resources/worker_resources.py	75.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1290      +/-   ##
===========================================
- Coverage    94.38%   86.87%   -7.52%     
===========================================
  Files           90       90              
  Lines         8262     8212      -50     
  Branches      1481     1456      -25     
===========================================
- Hits          7798     7134     -664     
- Misses         276      888     +612     
- Partials       188      190       +2     

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