fix: don't use spanId from invalid parent

[Flarna]

Don't use the spanId as parent in case the SpanContext is invalid.

[codecov]

Codecov Report

Merging #2105 (144caba) into main (181f11e) will decrease coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #2105      +/-   ##
==========================================
- Coverage   92.75%   92.73%   -0.03%     
==========================================
  Files         138      138              
  Lines        4927     4927              
  Branches     1017     1016       -1     
==========================================
- Hits         4570     4569       -1     
- Misses        357      358       +1     

Impacted Files	Coverage Δ
packages/opentelemetry-tracing/src/Tracer.ts	100.00% <100.00%> (ø)
...emetry-core/src/platform/node/RandomIdGenerator.ts	87.50% <0.00%> (-6.25%)	⬇️