Bugfix: check_availability(), negative last updated date

[Magnus167]

Bug #913 causing some problems

[codecov]

Codecov Report

Merging #928 (584a638) into develop (cb8b7ea) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

❗ Current head 584a638 differs from pull request most recent head 1c97df0. Consider uploading reports for the commit 1c97df0 to get more accurate results

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #928      +/-   ##
===========================================
- Coverage    74.49%   74.48%   -0.01%     
===========================================
  Files           31       31              
  Lines         3834     3833       -1     
===========================================
- Hits          2856     2855       -1     
  Misses         978      978              

Files Changed	Coverage Δ
macrosynergy/management/check_availability.py	46.87% <100.00%> (-0.82%)	⬇️