Fix UB and error propagation when X509_gmtime_adj() fails

[ndossche]

This causes UB later on when the certificate is passed to another function:

/work/php-src/Zend/zend_string.h:191:2: runtime error: null pointer passed as argument 2, which is declared to never be null
    #0 0x55cfb9407d94 in zend_string_init /work/php-src/Zend/zend_string.h:191
    #1 0x55cfb941ceb6 in add_assoc_stringl_ex /work/php-src/Zend/zend_API.c:1986
    #2 0x55cfb7f4c16d in add_assoc_stringl /work/php-src/Zend/zend_API.h:579
    #3 0x55cfb7f4cccd in php_openssl_add_assoc_asn1_string /work/php-src/ext/openssl/openssl_backend_common.c:113
    #4 0x55cfb7f2eb98 in zif_openssl_x509_parse /work/php-src/ext/openssl/openssl.c:1074
    #5 0x55cfb9160993 in zend_test_execute_internal /work/php-src/ext/zend_test/observer.c:306
    #6 0x55cfb958ee2d in ZEND_DO_FCALL_SPEC_RETVAL_USED_HANDLER /work/php-src/Zend/zend_vm_execute.h:2154
    #7 0x55cfb97854bd in execute_ex /work/php-src/Zend/zend_vm_execute.h:116519
    #8 0x55cfb9795c96 in zend_execute /work/php-src/Zend/zend_vm_execute.h:121962
    #9 0x55cfb99666c6 in zend_execute_script /work/php-src/Zend/zend.c:1980
    #10 0x55cfb919583e in php_execute_script_ex /work/php-src/main/main.c:2645
    #11 0x55cfb9195b48 in php_execute_script /work/php-src/main/main.c:2685
    #12 0x55cfb996bf48 in do_cli /work/php-src/sapi/cli/php_cli.c:951
    #13 0x55cfb996e6a1 in main /work/php-src/sapi/cli/php_cli.c:1362
    #14 0x7fb0b68301c9  (/lib/x86_64-linux-gnu/libc.so.6+0x2a1c9) (BuildId: 274eec488d230825a136fa9c4d85370fed7a0a5e)
    #15 0x7fb0b683028a in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x2a28a) (BuildId: 274eec488d230825a136fa9c4d85370fed7a0a5e)
    #16 0x55cfb7e097d4 in _start (/work/php-src/build-dbg-ubsan/sapi/cli/php+0x14097d4) (BuildId: b2b405964cc047ab6da19abaf92a8899a99e4a47)

Furthermore, it also simply does not propagate the error to userland.

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