fix: better handle corner cases for pre-IETF-64 agenda redirects

[jennifer-richards]

Fixes #3669

[codecov]

Codecov Report

Merging #3775 (3a61b58) into feat/bs5 (491cddb) will increase coverage by 0.00%.
The diff coverage is 70.58%.

❗ Current head 3a61b58 differs from pull request most recent head 1c20f5a. Consider uploading reports for the commit 1c20f5a to get more accurate results

@@            Coverage Diff            @@
##           feat/bs5    #3775   +/-   ##
=========================================
  Coverage     87.96%   87.97%           
=========================================
  Files           296      296           
  Lines         38795    38801    +6     
=========================================
+ Hits          34127    34134    +7     
+ Misses         4668     4667    -1     

Impacted Files	Coverage Δ
ietf/meeting/views.py	90.73% <66.66%> (+0.14%)	⬆️
ietf/meeting/helpers.py	90.58% <100.00%> (+0.01%)	⬆️
ietf/utils/draft.py	67.84% <0.00%> (-0.30%)	⬇️
ietf/group/utils.py	94.60% <0.00%> (+0.49%)	⬆️

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