Don't apply Scope's transaction name if it's empty

[st0012]

Fixes #1540.

[codecov-commenter]

Codecov Report

Merging #1546 (1e1b46f) into master (af9803a) will increase coverage by 0.36%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1546      +/-   ##
==========================================
+ Coverage   97.89%   98.25%   +0.36%     
==========================================
  Files         222      127      -95     
  Lines       10833     7001    -3832     
==========================================
- Hits        10605     6879    -3726     
+ Misses        228      122     -106     

Impacted Files	Coverage Δ
sentry-ruby/lib/sentry/scope.rb	100.00% <100.00%> (ø)
sentry-ruby/spec/sentry/transaction_spec.rb	100.00% <100.00%> (ø)
sentry-raven/lib/raven/instance.rb
sentry-raven/lib/raven/utils/real_ip.rb
sentry-raven/spec/raven/utils/request_id_spec.rb
sentry-raven/lib/raven/integrations/sidekiq.rb
sentry-raven/spec/raven/linecache_spec.rb
...ntry-raven/lib/raven/core_ext/object/duplicable.rb
...y-raven/lib/raven/integrations/rails/active_job.rb
sentry-raven/spec/raven/instance_spec.rb
... and 87 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update af9803a...1e1b46f. Read the comment docs.