Fix issue with flask url handler returning an iterator.

[weimzh]

If the iterator does some actual job then yield's part of response, sentry sdk would not catch anything after the url handler itself returned, and will miss everything being done in the iterator. This fixes the issue.

[sentrivana]

Heya @weimzh, thanks for the PR! Just looking at the code the changes look good to me. Also tested locally with a small Flask app that has an iterator response that throws an exception eventually, and the SDK captures it with your diff. So that looks good.

However, it looks like the change breaks quite a number of tests so we'll need to fix that. Do you have time to look into it?

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 79.54%. Comparing base (1bd744d) to head (3fedc7e).

Files with missing lines	Patch %	Lines
sentry_sdk/integrations/wsgi.py	50.00%	1 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3755      +/-   ##
==========================================
- Coverage   79.87%   79.54%   -0.33%     
==========================================
  Files         137      137              
  Lines       15371    15376       +5     
  Branches     2608     2611       +3     
==========================================
- Hits        12277    12231      -46     
- Misses       2223     2277      +54     
+ Partials      871      868       -3     

Files with missing lines	Coverage Δ
sentry_sdk/integrations/wsgi.py	81.33% <50.00%> (-3.50%)	⬇️

... and 17 files with indirect coverage changes