Documentation: Specify the constraint of the 'completed' parameter

Closes #482

Signed-off-by: Chris Dickens <christopher.a.dickens@gmail.com>

libusb/io.c

diff --git a/libusb/io.c b/libusb/io.c
index b95c382..54bef8a 100644
--- a/libusb/io.c
+++ b/libusb/io.c
@@ -920,6 +920,11 @@
  * do is submit a single transfer and wait for its completion, then using
  * one of the synchronous I/O functions is much easier.
  *
+ * \note
+ * The `completed` variable must be modified while holding the event lock,
+ * otherwise a race condition can still exist. It is simplest to do so from
+ * within the transfer callback as shown above.
+ *
  * \section eventlock The events lock
  *
  * The problem is when we consider the fact that libusb exposes file

libusb/version_nano.h

diff --git a/libusb/version_nano.h b/libusb/version_nano.h
index 1c9bd62..0ffc182 100644
--- a/libusb/version_nano.h
+++ b/libusb/version_nano.h
@@ -1 +1 @@
-#define LIBUSB_NANO 11546
+#define LIBUSB_NANO 11547