hotplug.c: Make sure hotplug buffer is NULL terminated

Sets the final byte explicitly to NULL because we later do string
operations on this buffer.

Fixes Coverity issue 1430926 String not null terminated

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>

plug/hotplug.c

@@ -545,11 +545,13 @@ static void hotplug_handler(struct uloop_fd *u, unsigned int ev)
 {
 	int i = 0;
 	static char buf[4096];
-	int len = recv(u->fd, buf, sizeof(buf), MSG_DONTWAIT);
+	int len = recv(u->fd, buf, sizeof(buf) - 1, MSG_DONTWAIT);
 	void *index;
 	if (len < 1)
 		return;
 
+	buf[len] = '\0';
+
 	blob_buf_init(&b, 0);
 	index = blobmsg_open_table(&b, NULL);
 	while (i < len) {