Handle None lineno in get_source_context

[sentrivana]

Be more defensive in get_source_context.

The current check makes no sense as we first try to decrement tb_lineno and then check the result against None:

    lineno = tb_lineno - 1
    if lineno is not None and abs_path:

So it looks like this was an oversight/got broken at some point.

Closes #3924

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 80.15%. Comparing base (57e9e51) to head (5e2b0f7).
Report is 2 commits behind head on master.

✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
sentry_sdk/utils.py	50.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3925      +/-   ##
==========================================
- Coverage   80.16%   80.15%   -0.02%     
==========================================
  Files         139      139              
  Lines       15391    15391              
  Branches     2596     2596              
==========================================
- Hits        12338    12336       -2     
  Misses       2208     2208              
- Partials      845      847       +2     

Files with missing lines	Coverage Δ
sentry_sdk/utils.py	83.71% <50.00%> (ø)

... and 2 files with indirect coverage changes

[antonpirker]

thumbs up!