Add missing libusb_exit on an error condition

Closes #448

Signed-off-by: Nathan Hjelm <hjelmn@lanl.gov>

examples/listdevs.c

diff --git a/examples/listdevs.c b/examples/listdevs.c
index 3328910..b5b027c 100644
--- a/examples/listdevs.c
+++ b/examples/listdevs.c
@@ -60,8 +60,10 @@
 		return r;
 
 	cnt = libusb_get_device_list(NULL, &devs);
-	if (cnt < 0)
+	if (cnt < 0){
+		libusb_exit(NULL);
 		return (int) cnt;
+	}
 
 	print_devs(devs);
 	libusb_free_device_list(devs, 1);

libusb/version_nano.h

diff --git a/libusb/version_nano.h b/libusb/version_nano.h
index 08264b3..8c03606 100644
--- a/libusb/version_nano.h
+++ b/libusb/version_nano.h
@@ -1 +1 @@
-#define LIBUSB_NANO 11321
+#define LIBUSB_NANO 11322