fix: handle allocation failure in cJSONUtils_FindPointerFromObjectTo

[xuh0923]

Issue
This change fixes a missing allocation failure check in cJSONUtils_FindPointerFromObjectTo.

When cJSON_malloc returns NULL while building the JSON pointer path, the function may dereference a null pointer before returning. That makes the failure path unsafe in low-memory situations.

Changes

• add missing NULL checks after allocating full_pointer in the array and object branches of cJSONUtils_FindPointerFromObjectTo
• add a regression test that uses failing hooks to verify the function returns NULL for both branches when allocation fails

Verification

• build and run tests/misc_utils_tests.c with gcc -Wall -Wextra -Werror -std=c89
• build and run tests/old_utils_tests.c with gcc -Wall -Wextra -Werror -std=c89