Fix memory leak on error path in openssl_open()

[ndossche]

pkey must be released after it was allocated on the error paths. Otherwise we get leaks like this:

Direct leak of 32 byte(s) in 1 object(s) allocated from:
    #0 0x7ff8d76a1340 in calloc ../../../../src/libsanitizer/asan/asan_malloc_linux.cpp:77
    #1 0x7ff8d7189136 in EVP_PKEY_new evp/p_lib.c:385
    #2 0x7ff8d71178e4 in d2i_PrivateKey asn1/a_pkey.c:80
    #3 0x7ff8d719ed07 in PEM_read_bio_PrivateKey pem/pem_pkey.c:135
    #4 0x555c54726e80 in php_openssl_pem_read_bio_private_key /work/php-src/ext/openssl/openssl_backend_v1.c:738
    #5 0x555c5471ee77 in php_openssl_pkey_from_zval /work/php-src/ext/openssl/openssl_backend_common.c:1297
    #6 0x555c54712e3f in zif_openssl_open /work/php-src/ext/openssl/openssl.c:4331
    #7 0x555c554b44e5 in zend_test_execute_internal /work/php-src/ext/zend_test/observer.c:306
    #8 0x555c557dba0b in ZEND_DO_FCALL_SPEC_RETVAL_UNUSED_HANDLER /work/php-src/Zend/zend_vm_execute.h:2024
    #9 0x555c5593cf57 in execute_ex /work/php-src/Zend/zend_vm_execute.h:116514
    #10 0x555c55951ec0 in zend_execute /work/php-src/Zend/zend_vm_execute.h:121962
    #11 0x555c55ab60cc in zend_execute_script /work/php-src/Zend/zend.c:1980
    #12 0x555c554e8ecb in php_execute_script_ex /work/php-src/main/main.c:2645
    #13 0x555c554e92db in php_execute_script /work/php-src/main/main.c:2685
    #14 0x555c55abbc37 in do_cli /work/php-src/sapi/cli/php_cli.c:951
    #15 0x555c55abe204 in main /work/php-src/sapi/cli/php_cli.c:1362
    #16 0x7ff8d6d061c9  (/lib/x86_64-linux-gnu/libc.so.6+0x2a1c9) (BuildId: 274eec488d230825a136fa9c4d85370fed7a0a5e)
    #17 0x7ff8d6d0628a in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x2a28a) (BuildId: 274eec488d230825a136fa9c4d85370fed7a0a5e)
    #18 0x555c54609db4 in _start (/work/php-src/build-dbg-asan/sapi/cli/php+0x609db4) (BuildId: 5cc444a6a9fc1a486ea698e72366c16bd5472605)

This was found by a hybrid static-dynamic analyser that looks for inconsistent handling of error checks in bindings.