curl: Function `do_pubkey()` can have out-of-bound read issue

Summary A 1-byte out-of-bounds heap read in dopubkey in lib/vtls/x509asn1.c. When parsing an RSA public key with a zero-length or all-zero modulus, the loop dereferences a pointer before checking bounds. Requires a non-OpenSSL TLS backend e.g., Mbed/Gnu. A certificate chain verification can trigg...