a fix for SIGSEGV in handle_bulk_completion()

We cannot dereference tpriv after calling
usbi_handle_transfer_cancellation() because that function may invoke
the user-supplied callback which may free the transfer.
diff --git a/AUTHORS b/AUTHORS
index 6e17e37..86d9a3f 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -2,6 +2,7 @@
 Copyright (c) 2001 Johannes Erdfelt <johannes@erdfelt.com>
 
 Other contributors:
+Artem Egorkine
 David Engraf
 Rob Walker
 Vasily Khoruzhick