[fix] Add null check for span.logs in search/filter-spans

[achesin]

Which problem is this PR solving?

• Hello! This is a small PR for a bug I found in on the Trace Page. In the Trace Page Search Bar when you type in something that does not correspond with a tag, the page crashes and goes all white. That is because there was nothing checking to make sure span.logs was populated.

Short description of the changes

• I added a check to make sure span.logs is not equal to null and a corresponding test.

[codecov]

Codecov Report

Merging #734 (91305e6) into master (ae758fa) will increase coverage by 0.03%.
The diff coverage is 100.00%.

❗ Current head 91305e6 differs from pull request most recent head 63c5d65. Consider uploading reports for the commit 63c5d65 to get more accurate results

@@            Coverage Diff             @@
##           master     #734      +/-   ##
==========================================
+ Coverage   94.39%   94.42%   +0.03%     
==========================================
  Files         230      230              
  Lines        5959     5959              
  Branches     1448     1448              
==========================================
+ Hits         5625     5627       +2     
+ Misses        300      298       -2     
  Partials       34       34              

Impacted Files	Coverage Δ
packages/jaeger-ui/src/utils/filter-spans.tsx	100.00% <100.00%> (ø)
...nents/TracePage/TraceTimelineViewer/SpanBarRow.tsx	79.31% <0.00%> (+6.89%)	⬆️

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[yurishkuro]

thanks