fix `resampling_iterations_idx` on singleton forecast

[aaronspring]

Description

Closes #375

Type of change

Please delete options that are not relevant.

• [x] Bug fix (non-breaking change which fixes an issue)

Checklist (while developing)

• [ ] I have commented my code, particularly in hard-to-understand areas
• [x] Tests added for pytest, if necessary.

[pep8speaks]

Hello @aaronspring! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

There are currently no PEP 8 issues detected in this Pull Request. Cheers! :beers:

Comment last updated at 2022-02-20 10:23:07 UTC

[codecov[bot]]

Codecov Report

Merging #376 (5392639) into main (b52cc3f) will increase coverage by 0.11%. The diff coverage is 94.80%.

:exclamation: Current head 5392639 differs from pull request most recent head cc3252b. Consider uploading reports for the commit cc3252b to get more accurate results

@@            Coverage Diff             @@
##             main     #376      +/-   ##
==========================================
+ Coverage   94.58%   94.70%   +0.11%     
==========================================
  Files          24       27       +3     
  Lines        2661     2812     +151     
==========================================
+ Hits         2517     2663     +146     
- Misses        144      149       +5     

Impacted Files	Coverage Δ
xskillscore/versioning/print_versions.py	16.66% <0.00%> (+0.66%)	:arrow_up:
xskillscore/core/comparative.py	87.00% <61.53%> (-4.31%)	:arrow_down:
xskillscore/core/np_deterministic.py	98.49% <80.00%> (-0.75%)	:arrow_down:
xskillscore/tests/test_probabilistic.py	96.76% <92.30%> (+0.04%)	:arrow_up:
xskillscore/core/probabilistic.py	89.85% <93.18%> (-0.50%)	:arrow_down:
xskillscore/core/stattests.py	97.29% <97.29%> (ø)
xskillscore/__init__.py	85.71% <100.00%> (+1.09%)	:arrow_up:
xskillscore/core/contingency.py	95.77% <100.00%> (+0.09%)	:arrow_up:
xskillscore/core/deterministic.py	97.74% <100.00%> (+0.05%)	:arrow_up:
xskillscore/core/np_probabilistic.py	100.00% <100.00%> (ø)
... and 6 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update 180b689...cc3252b. Read the comment docs.

[raybellwaves]

LGTM thanks