libzfs_sendrecv: Initialize in case of failure

In zfs_send_progress, initialize \*bytes_written and \*blocks_visited
in case we have to return early due to ioctl failure.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ryan Moeller <freqlabs@FreeBSD.org>
Closes openzfs#12967

lib/libzfs/libzfs_sendrecv.c

@@ -883,6 +883,10 @@ zfs_send_progress(zfs_handle_t *zhp, int fd, uint64_t *bytes_written,
 {
 	zfs_cmd_t zc = {"\0"};
 
+	if (bytes_written != NULL)
+		*bytes_written = 0;
+	if (blocks_visited != NULL)
+		*blocks_visited = 0;
 	(void) strlcpy(zc.zc_name, zhp->zfs_name, sizeof (zc.zc_name));
 	zc.zc_cookie = fd;
 	if (zfs_ioctl(zhp->zfs_hdl, ZFS_IOC_SEND_PROGRESS, &zc) != 0)