Core: Don't wait for completion if cancel_transfer failed

* See http://libusbx.1081486.n5.nabble.com/Libusbx-devel-libusb-interrupt-transfer-does-not-return-in-case-of-error-td626.html
* Closes #76
diff --git a/AUTHORS b/AUTHORS
index cb0511a..88c7ab5 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -48,4 +48,5 @@
 Vasily Khoruzhick
 Vitali Lovich
 Xiaofan Chen
+Zoltán Kovács
 Роман Донченко