fix: defensively handle null source address in MassTransit instrumentation

[nr-ahemsath]

BEGIN_COMMIT_OVERRIDE
fix: Defensively handle null source address in MassTransit instrumentation. (#2055)
END_COMMIT_OVERRIDE

Fixes #2055 by checking for a null source address before attempting to use it to get the queue name and type. If the source address is null, the queue name will be "Unknown" and the type will be "Queue".

I added a story to the backlog to revisit the issue of queue naming when time permits: #2061

[codecov-commenter]

Codecov Report

Merging #2060 (dabf9a6) into main (d0b8d26) will decrease coverage by 0.01%.
Report is 2 commits behind head on main.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2060      +/-   ##
==========================================
- Coverage   81.06%   81.05%   -0.01%     
==========================================
  Files         394      395       +1     
  Lines       24678    24697      +19     
  Branches     2963     2966       +3     
==========================================
+ Hits        20004    20017      +13     
- Misses       3889     3892       +3     
- Partials      785      788       +3     

Files	Coverage Δ
...s/NewRelic.Agent.Extensions/Helpers/MassTransit.cs	100.00% <100.00%> (ø)

... and 2 files with indirect coverage changes