Correct a type error in the usage of Commit^ivk: the output type Commit^ivk.Output includes 0, but the type of incoming viewing keys should not include 0 because KA^Orchard.Private does not. This is now handled by explicitly rejecting 0 as output from Commit^ivk when generating ivk in \crossref{orchardkeycomponents}.
Correct a type error in the usage of Commit^ivk: the output type Commit^ivk.Output includes 0,
but the type of incoming viewing keys should not include 0 because KA^Orchard.Private does not.
This is now handled by explicitly rejecting 0 as output from Commit^ivk when generating ivk
in \crossref{orchardkeycomponents}.

An encoding of ivk as 0 is also rejected in \crossref{orchardinviewingkeyencoding} when parsing
an incoming viewing key.

The action circuit needed no changes because pk_d already could not be the zero point, and
therefore the 'Diversified address integrity' condition fails when ivk = 0.

Signed-off-by: Daira Hopwood <cd7d43d5556a38ce626d53826fddc46adc597539@jacaranda.org>

zcash/zips,zcash/zips,zcash/zips,zcash/zips