Fixes exception in django cause by long iter check

[karthiknadig]

fixes #406
fixes #423

[codecov-io]

Codecov Report

Merging #443 into master will increase coverage by 0.07%.
The diff coverage is 75%.

@@            Coverage Diff            @@
##           master    #443      +/-   ##
=========================================
+ Coverage   59.03%   59.1%   +0.07%     
=========================================
  Files          26      26              
  Lines        3466    3470       +4     
=========================================
+ Hits         2046    2051       +5     
+ Misses       1420    1419       -1

Impacted Files	Coverage Δ
ptvsd/safe_repr.py	79.39% <75%> (-0.61%)	⬇️
ptvsd/ipcjson.py	67.11% <0%> (+1.33%)	⬆️

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