fix: Skip UI crumbs when target or sender is nil

[philipphofmann]

📜 Description

Skip adding breadcrumbs when sendAction is called with either target or sender being nil. This fixes an issue with a third-party library calling sendAction with target being nil in a tight loop.

💡 Motivation and Context

Fixes GH-4019

💚 How did you test it?

Unit test.

📝 Checklist

You have to check all boxes before merging:

• I reviewed the submitted code.
• I added tests to verify the changes.
• No new PII added or SDK only sends newly added PII if sendDefaultPII is enabled.
• I updated the docs if needed.
• Review from the native team if needed.
• No breaking change or entry added to the changelog.
• No breaking change for hybrid SDKs or communicated to hybrid SDKs.

🔮 Next steps

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.416%. Comparing base (fe89531) to head (a12b866).
Report is 2 commits behind head on main.

Additional details and impacted files

@@              Coverage Diff              @@
##              main     #4211       +/-   ##
=============================================
+ Coverage   91.408%   91.416%   +0.008%     
=============================================
  Files          611       611               
  Lines        49024     49035       +11     
  Branches     17702     17688       -14     
=============================================
+ Hits         44812     44826       +14     
+ Misses        4120      4116        -4     
- Partials        92        93        +1     

Files	Coverage Δ
Sources/Sentry/SentryBreadcrumbTracker.m	77.181% <100.000%> (+0.990%)	⬆️
...ons/Breadcrumbs/SentryBreadcrumbTrackerTests.swift	93.589% <100.000%> (+0.439%)	⬆️

... and 3 files with indirect coverage changes

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[github-actions]

Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	1220.65 ms	1238.78 ms	18.12 ms
Size	21.58 KiB	694.19 KiB	672.60 KiB

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
d760c3f	1228.58 ms	1246.22 ms	17.64 ms
3f74b8f	1229.90 ms	1249.42 ms	19.52 ms
983de17	1260.57 ms	1263.68 ms	3.11 ms
5d6ce0e	1206.72 ms	1228.67 ms	21.95 ms
bd2afa6	1192.31 ms	1210.37 ms	18.05 ms
1e065bc	1239.69 ms	1258.18 ms	18.49 ms
3478fc5	1237.94 ms	1251.13 ms	13.19 ms
3297d6e	1196.08 ms	1205.43 ms	9.35 ms
5be7a7c	1223.25 ms	1237.12 ms	13.87 ms
a176fc4	1250.29 ms	1257.88 ms	7.59 ms

App size

Revision	Plain	With Sentry	Diff
d760c3f	22.84 KiB	403.17 KiB	380.33 KiB
3f74b8f	21.58 KiB	418.78 KiB	397.20 KiB
983de17	22.84 KiB	403.19 KiB	380.34 KiB
5d6ce0e	22.85 KiB	405.38 KiB	382.53 KiB
bd2afa6	20.76 KiB	420.55 KiB	399.79 KiB
1e065bc	20.76 KiB	425.78 KiB	405.01 KiB
3478fc5	21.58 KiB	654.59 KiB	633.01 KiB
3297d6e	21.58 KiB	418.44 KiB	396.86 KiB
5be7a7c	21.58 KiB	671.89 KiB	650.31 KiB
a176fc4	22.84 KiB	403.24 KiB	380.39 KiB