Update sabre/xml to fix XML parsing errors (with empty strings)

Signed-off-by: Christoph Wurst <christoph@winzerhof-wurst.at>

diff --git a/3rdparty b/3rdparty
index a7e8c63bac637bbb5ff469224d09a6acaefecf4d..8d7a96cde06a0357ce5805e00773b576d7595ef8 160000 (submodule)
--- a/3rdparty
+++ b/3rdparty
@@ -1 +1 @@
-Subproject commit a7e8c63bac637bbb5ff469224d09a6acaefecf4d
+Subproject commit 8d7a96cde06a0357ce5805e00773b576d7595ef8