libusb: consider bad fd as a broken event

Application can use libusb_get_pollfds to get pollfds from libusb then
close the fd themselves. This cause the hotplug thread unable to leave
because it will be consider as a invalid event then loop forever instead
of a broken event that should be quit immediately.

Reviewed by: bapt
Sponsored by: FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D50959

lib/libusb/libusb10_hotplug.c

@@ -140,6 +140,8 @@ verify_event_validity(libusb_context *ctx)
 				return (valid_event);
 			return (invalid_event);
 		}
+		if (errno == EBADF)
+			return (broken_event);
 		return (invalid_event);
 	} else if (ctx->usb_event_mode == usb_event_devd) {
 		char buf[DEVCTL_MAXBUF];