Update to libxml2 2.9.9 (2019-01-03).

Test: builds and boots
Change-Id: Ia2f383beeb2f6af715e2c44b546ded594f523dc4
diff --git a/xmlIO.c b/xmlIO.c
index 8254347..f61dd05 100644
--- a/xmlIO.c
+++ b/xmlIO.c
@@ -3157,7 +3157,7 @@
 	 * convert as much as possible to the parser reading buffer.
 	 */
 	use = xmlBufUse(in->raw);
-	nbchars = xmlCharEncInput(in, 0);
+	nbchars = xmlCharEncInput(in, 1);
 	if (nbchars < 0) {
 	    xmlIOErr(XML_IO_ENCODER, NULL);
 	    in->error = XML_IO_ENCODER;
@@ -3273,7 +3273,7 @@
 	 * convert as much as possible to the parser reading buffer.
 	 */
 	use = xmlBufUse(in->raw);
-	nbchars = xmlCharEncInput(in, 0);
+	nbchars = xmlCharEncInput(in, 1);
 	if (nbchars < 0) {
 	    xmlIOErr(XML_IO_ENCODER, NULL);
 	    in->error = XML_IO_ENCODER;