Fix NULL deref when enabling TLS fails and the peer name needs to be reset

The code tries to read the context on NULL when
`php_stream_xport_crypto_setup` fails because by then `stream` is reset
to NULL.
This is also UB, so can cause miscompiles.

```
==1217==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000090 (pc 0x55d829ed3acf bp 0x7fff045f5770 sp 0x7fff045f4df0 T0)
==1217==The signal is caused by a READ memory access.
==1217==Hint: address points to the zero page.
    #0 0x55d829ed3acf in php_stream_url_wrap_http_ex /work/php-src/ext/standard/http_fopen_wrapper.c:580
    #1 0x55d829ed857e in php_stream_url_wrap_http /work/php-src/ext/standard/http_fopen_wrapper.c:1204
    #2 0x55d82a15073d in _php_stream_open_wrapper_ex /work/php-src/main/streams/streams.c:2270
    #3 0x55d829e78fa6 in zif_file_get_contents /work/php-src/ext/standard/file.c:409
    #4 0x55d829bbfe39 in zif_phar_file_get_contents /work/php-src/ext/phar/func_interceptors.c:226
    #5 0x55d82a0b7ed2 in zend_test_execute_internal /work/php-src/ext/zend_test/observer.c:306
    #6 0x55d82a3e024a in ZEND_DO_FCALL_SPEC_RETVAL_USED_HANDLER /work/php-src/Zend/zend_vm_execute.h:2154
    #7 0x55d82a540995 in execute_ex /work/php-src/Zend/zend_vm_execute.h:116519
    #8 0x55d82a5558b0 in zend_execute /work/php-src/Zend/zend_vm_execute.h:121962
    #9 0x55d82a6ba0ab in zend_execute_script /work/php-src/Zend/zend.c:1980
    #10 0x55d82a0ec8bb in php_execute_script_ex /work/php-src/main/main.c:2645
    #11 0x55d82a0ecccb in php_execute_script /work/php-src/main/main.c:2685
    #12 0x55d82a6bfc16 in do_cli /work/php-src/sapi/cli/php_cli.c:951
    #13 0x55d82a6c21e3 in main /work/php-src/sapi/cli/php_cli.c:1362
    #14 0x7f9e770491c9  (/lib/x86_64-linux-gnu/libc.so.6+0x2a1c9) (BuildId: 274eec488d230825a136fa9c4d85370fed7a0a5e)
    #15 0x7f9e7704928a in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x2a28a) (BuildId: 274eec488d230825a136fa9c4d85370fed7a0a5e)
    #16 0x55d829209b34 in _start (/work/php-src/build-dbg-asan/sapi/cli/php+0x609b34) (BuildId: aa149f943514fff0c491e1f199e30fed0e977f7c)
```

Author: ndossche

ext/standard/http_fopen_wrapper.c

@@ -561,16 +561,18 @@ static php_stream *php_stream_url_wrap_http_ex(php_stream_wrapper *wrapper,
 
 		/* enable SSL transport layer */
 		if (stream) {
+			php_stream_context *old_context = PHP_STREAM_CONTEXT(stream);
+
 			if (php_stream_xport_crypto_setup(stream, STREAM_CRYPTO_METHOD_SSLv23_CLIENT, NULL) < 0 ||
 			    php_stream_xport_crypto_enable(stream, 1) < 0) {
 				php_stream_wrapper_log_error(wrapper, options, "Cannot connect to HTTPS server through proxy");
 				php_stream_close(stream);
 				stream = NULL;
 			}
-		}
 
-		if (reset_ssl_peer_name) {
-			php_stream_context_unset_option(PHP_STREAM_CONTEXT(stream), "ssl", "peer_name");
+			if (reset_ssl_peer_name) {
+				php_stream_context_unset_option(old_context, "ssl", "peer_name");
+			}
 		}
 	}