Fix: Set current thread only if theres no exceptions

[marandaneto]

📢 Type of change

• Bugfix
• New feature
• Enhancement
• Refactoring

📜 Description

Fix: Set current thread only if theres no exceptions

💡 Motivation and Context

We'd like to set the default (current) thread if attachStacktrace is enabled and there are no exceptions only, exceptions have its own stack traces already.
one of the use cases for this is events captured by hybrid SDKs like React-native or Flutter, the current thread will be always the File observer, and it doesn't make much sense.

💚 How did you test it?

📝 Checklist

• I reviewed submitted code
• I added tests to verify changes
• All tests passing
• No breaking changes

🔮 Next steps

[marandaneto]

This also helps with #984

[maciejwalkowiak]

LGTM

[codecov-io]

Codecov Report

Merging #1064 (f05d1eb) into main (e33333b) will increase coverage by 0.00%.
The diff coverage is 83.33%.

@@            Coverage Diff            @@
##               main    #1064   +/-   ##
=========================================
  Coverage     72.95%   72.96%           
- Complexity     1520     1523    +3     
=========================================
  Files           161      161           
  Lines          5461     5463    +2     
  Branches        550      551    +1     
=========================================
+ Hits           3984     3986    +2     
  Misses         1187     1187           
  Partials        290      290           

Impacted Files	Coverage Δ	Complexity Δ
...ry/src/main/java/io/sentry/MainEventProcessor.java	77.35% <81.81%> (+0.88%)	18.00 <1.00> (+3.00)
...y/src/main/java/io/sentry/SentryThreadFactory.java	97.14% <100.00%> (ø)	13.00 <0.00> (ø)

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[bruno-garcia]

Thanks!