fix: Crash when reading corrupted envelope

[brustolin]

📜 Description

Added a safe guard to prevent crashing when reading corrupted envelope

💡 Motivation and Context

This was mentioned in #4280

💚 How did you test it?

Unit tests

📝 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

[github-actions]

Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	1210.73 ms	1245.63 ms	34.90 ms
Size	21.58 KiB	706.70 KiB	685.12 KiB

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
135dec6	1236.67 ms	1255.13 ms	18.45 ms
42f4107	1224.52 ms	1244.77 ms	20.25 ms
25bcc50	1237.69 ms	1258.40 ms	20.71 ms
253bb71	1221.62 ms	1250.82 ms	29.20 ms
699d76f	1217.12 ms	1236.33 ms	19.20 ms
4b1113e	1239.04 ms	1250.45 ms	11.41 ms
7cd187e	1239.39 ms	1258.02 ms	18.63 ms
e758449	1243.41 ms	1246.71 ms	3.31 ms
aa4eddf	1228.21 ms	1236.72 ms	8.51 ms
06bac56	1213.62 ms	1236.27 ms	22.65 ms

App size

Revision	Plain	With Sentry	Diff
135dec6	21.58 KiB	615.19 KiB	593.61 KiB
42f4107	21.58 KiB	614.92 KiB	593.34 KiB
25bcc50	20.76 KiB	427.23 KiB	406.46 KiB
253bb71	20.76 KiB	393.37 KiB	372.60 KiB
699d76f	21.58 KiB	631.82 KiB	610.24 KiB
4b1113e	21.58 KiB	697.83 KiB	676.25 KiB
7cd187e	20.76 KiB	401.65 KiB	380.89 KiB
e758449	22.85 KiB	407.62 KiB	384.77 KiB
aa4eddf	21.58 KiB	544.86 KiB	523.28 KiB
06bac56	22.84 KiB	403.23 KiB	380.39 KiB

Previous results on branch: fix/unserialize-envelope-item

Startup times

Revision	Plain	With Sentry	Diff
83979c7	1230.82 ms	1248.88 ms	18.06 ms

App size

Revision	Plain	With Sentry	Diff
83979c7	21.58 KiB	706.78 KiB	685.20 KiB

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.696%. Comparing base (a0cc9d6) to head (8966958).
Report is 1 commits behind head on main.

Additional details and impacted files

@@              Coverage Diff              @@
##              main     #4297       +/-   ##
=============================================
+ Coverage   91.684%   91.696%   +0.011%     
=============================================
  Files          617       617               
  Lines        50194     50205       +11     
  Branches     18116     18119        +3     
=============================================
+ Hits         46020     46036       +16     
+ Misses        4083      4076        -7     
- Partials        91        93        +2     

Files	Coverage Δ
Sources/Sentry/SentrySerialization.m	92.018% <100.000%> (+0.191%)	⬆️
.../SentryTests/Helper/SentrySerializationTests.swift	98.507% <100.000%> (+0.045%)	⬆️

... and 9 files with indirect coverage changes

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