btrfs: tree-checker: validate number of chunk stripes and parity

If there's no parity and num_stripes < ncopies, a crafted image can
trigger a division by zero in calc_stripe_length().

The image was generated through fuzzing.

CC: stable@vger.kernel.org # 5.4+
Reviewed-by: Qu Wenruo <wqu@suse.com>
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=209587


Signed-off-by: Daniel Xu <dxu@dxuuu.xyz>
Signed-off-by: David Sterba <dsterba@suse.com>