Address Scrutinice findings

[justsmth]

Issues:

Addresses P188794065

Description of changes:

• Cleanup a few issues identified through static anaylsis

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license and the ISC license.

[jakemas]

Thank you!

[jakemas]

free_der.reset(der) is still used in a few more spots:

• aws-lc/crypto/evp_extra/evp_extra_test.cc

  Line 1622 in d04c818

  free_der.reset(der);

• aws-lc/crypto/evp_extra/evp_extra_test.cc

  Line 1629 in d04c818

  free_der.reset(der);

• aws-lc/crypto/x509/x509_test.cc

  Line 7503 in d04c818

  free_der.reset(der);