Fix segfault if the JSON parser cannot parse the JWKS

[jthiltges]

Ensure m_cget is still valid when building the exception text with m_cget->get_url().

If the issuer published a JWKS that's not valid JSON, it triggers an exception. The unique_ptr is accessed to build the exception text. Move the reset() to after the exception to avoid a segfault.

scitokens::internal::SimpleCurlGet::get_url[abi:cxx11]() const (this=0x0) at /tmp/mnt/src/scitokens_internal.cpp:108
108         if (!m_curl) {
(gdb) bt
#0  scitokens::internal::SimpleCurlGet::get_url[abi:cxx11]() const (this=0x0) at /tmp/mnt/src/scitokens_internal.cpp:108
#1  0x00007f4f4997b293 in scitokens::Validator::get_public_keys_from_web_continue (status=...) at /tmp/mnt/src/scitokens_internal.cpp:741
#2  0x00007f4f4999a267 in scitokens::Validator::refresh_jwks (issuer=...) at /usr/local/include/c++/14.2.0/bits/unique_ptr.h:191
#3  0x00007f4f4997e90f in keycache_refresh_jwks (issuer=0x4f4898 "https://t2.unl.edu/jthiltge/issuer/invalid", err_msg=0x7ffe0145bec0) at /usr/local/include/c++/14.2.0/bits/basic_string.tcc:242

[Copilot]

Pull Request Overview

This PR fixes a critical bug that would cause a null pointer dereference during error handling in the public key download process.

• Moved status->m_cget.reset() call to after the JSON parsing error check to prevent accessing a null pointer in error messages

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