crypto: check for nullptr before dereferencing identity_buf

[gurgunday]

The js-side already checks for this so the test already passes, so I don't think it's a vulnerability

Just in case, added the check for future

Fix #56665

[nodejs-github-bot]

Review requested:

• @nodejs/crypto

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 90.26%. Comparing base (e2bc395) to head (3d9278e).
Report is 36 commits behind head on main.

Files with missing lines	Patch %	Lines
src/crypto/crypto_tls.cc	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #57071      +/-   ##
==========================================
- Coverage   90.37%   90.26%   -0.11%     
==========================================
  Files         629      630       +1     
  Lines      184365   184634     +269     
  Branches    36016    36131     +115     
==========================================
+ Hits       166612   166666      +54     
- Misses      10918    11025     +107     
- Partials     6835     6943     +108     

Files with missing lines	Coverage Δ
src/crypto/crypto_tls.cc	78.16% <0.00%> (ø)

... and 51 files with indirect coverage changes

[gurgunday]

Don't know how to test this since any js code would have its argument validated before moving to the C++ side

[gurgunday]

Rebased

[gurgunday]

CI failures seem unrelated?

[gurgunday]

Yeah seems to be random this CI failure, it was linux and now it's macos

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/65391/

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/65433/

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/65469/