BF: Make sure to not issue an install-ok result, before the repo state is final

[mih]

The underlying issue was discovered in #3903

[codecov]

Codecov Report

Merging #3906 into master will increase coverage by 9.7%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master    #3906     +/-   ##
=========================================
+ Coverage   71.01%   80.71%   +9.7%     
=========================================
  Files         272      272             
  Lines       36065    36066      +1     
=========================================
+ Hits        25611    29112   +3501     
+ Misses      10454     6954   -3500

Impacted Files	Coverage Δ
datalad/distribution/get.py	85.43% <100%> (+66.41%)	⬆️
datalad/downloaders/tests/test_http.py	58.08% <0%> (-2.21%)	⬇️
datalad/support/tests/test_gitrepo.py	99.89% <0%> (+0.1%)	⬆️
datalad/distribution/tests/test_install.py	99.79% <0%> (+0.2%)	⬆️
datalad/interface/tests/test_rerun.py	100% <0%> (+0.4%)	⬆️
datalad/log.py	65.86% <0%> (+0.48%)	⬆️
datalad/tests/test_config.py	100% <0%> (+1.19%)	⬆️
datalad/downloaders/http.py	61.35% <0%> (+1.19%)	⬆️
datalad/core/local/tests/test_save.py	99.19% <0%> (+1.34%)	⬆️
datalad/metadata/tests/test_search.py	94.96% <0%> (+1.43%)	⬆️
... and 70 more

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[mih]

Rebased on master after merge of #3904. Could not replicate any of the windows test failures on a win10 box with Git 2.23.

[bpoldrack]

Looks right.

[mih]

Cool, thanks!