use ZEND_U_CONVERTER() macro to prevent segfaults when the converter is not set (i.e. NULL)

ext/session/mod_files.c

@@ -127,7 +127,7 @@ static char *ps_files_path_create(char *buf, size_t buflen, ps_files *data, cons
 		int newlen;
 		UErrorCode status = U_ZERO_ERROR;
 
-		zend_convert_encodings(UG(filesystem_encoding_conv), UG(utf8_conv), &newbuf, &newlen, buf, n, &status);
+		zend_convert_encodings(ZEND_U_CONVERTER(UG(filesystem_encoding_conv)), UG(utf8_conv), &newbuf, &newlen, buf, n, &status);
 
 		if (status != U_ZERO_ERROR) {
 			php_error_docref(NULL TSRMLS_CC, E_NOTICE, "Failure converting savepath to local filesystem encoding, attempting to use utf8");

ext/sysvmsg/sysvmsg.c

@@ -413,7 +413,7 @@ PHP_FUNCTION(msg_send)
 		char *p = NULL;
 		switch (Z_TYPE_P(message)) {
 			case IS_UNICODE:
-				if (SUCCESS != zend_unicode_to_string(UG(runtime_encoding_conv), &p, &message_len, Z_USTRVAL_P(message), Z_USTRLEN_P(message) TSRMLS_CC)) {
+				if (SUCCESS != zend_unicode_to_string(ZEND_U_CONVERTER(UG(runtime_encoding_conv)), &p, &message_len, Z_USTRVAL_P(message), Z_USTRLEN_P(message) TSRMLS_CC)) {
 					RETURN_FALSE;
 				}
 				break;