Port XML_GetCurrentByteIndex to public APIs

This is necessary to avoid a deprecation break in libxml2 2.14.x.

Author: nielsdos

ext/xml/compat.c

@@ -705,8 +705,21 @@ XML_GetCurrentColumnNumber(XML_Parser parser)
 PHP_XML_API int
 XML_GetCurrentByteIndex(XML_Parser parser)
 {
-	return parser->parser->input->consumed +
-			(parser->parser->input->cur - parser->parser->input->base);
+	/* We have to temporarily disable the encoder to satisfy the note from the manual:
+	 * "This function returns byte index according to UTF-8 encoded text disregarding if input is in another encoding."
+	 * Although that should probably be corrected at one point? (TODO) */
+	xmlCharEncodingHandlerPtr encoder = NULL;
+	xmlParserInputPtr input = parser->parser->input;
+	if (input->buf) {
+		encoder = input->buf->encoder;
+		input->buf->encoder = NULL;
+	}
+	long result = xmlByteConsumed(parser->parser);
+	if (encoder) {
+		input->buf->encoder = encoder;
+	}
+	/* TODO: at one point this should return long probably to make sure that files greater than 2 GiB are handled correctly. */
+	return (int) result;
 }
 
 PHP_XML_API int