[FIX] Fail gracefully on RequestError

[ppfeufer]

Description

Fixed

• Fail gracefully on RequestError, which can be thrown by django-esi when ESI is
  unavailable, instead of crashing the task (Downtime, Endpoint down, etc.)

Type of Change:

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality not to work as expected)

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented on my code, particularly in hard-to-understand areas
• I have checked my code and corrected any misspellings

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (ced9eda) to head (2486239).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##            master      #322   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           10        10           
  Lines          309       309           
  Branches        18        18           
=========================================
  Hits           309       309           

Files with missing lines	Coverage Δ
sovtimer/providers.py	100.00% <100.00%> (ø)

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