Ensure the channel poll callback is called with len 0 on error.

[meshlink] / src / utcp

diff --git a/src/utcp b/src/utcp
index d394c4f4f9b820cb1866046e21b834b67fd18ecb..275129c9d08b2d29529b2f9d039198168aeb52a7 160000 (submodule)
--- a/src/utcp
+++ b/src/utcp
@@ -1 +1 @@
-Subproject commit d394c4f4f9b820cb1866046e21b834b67fd18ecb
+Subproject commit 275129c9d08b2d29529b2f9d039198168aeb52a7