Simplify a few pattern matches

A few pattern-matches correspond directly to standard combinators on
`Result`, `Option`. This uses them for concision / clarity.

Refactorings reviewed by the author after suggestion from [comby-rust](https://github.com/huitseeker/comby-rust).

zcash_primitives/src/transaction/builder.rs

@@ -123,10 +123,7 @@ impl SaplingOutput {
         value: Amount,
         memo: Option<Memo>,
     ) -> Result<Self, Error> {
-        let g_d = match to.g_d() {
-            Some(g_d) => g_d,
-            None => return Err(Error::InvalidAddress),
-        };
+        let g_d = to.g_d().ok_or(Error::InvalidAddress)?;
         if value.is_negative() {
             return Err(Error::InvalidAmount);
         }

zcash_primitives/src/zip32.rs

@@ -429,10 +429,7 @@ impl ExtendedFullViewingKey {
     }
 
     pub fn address(&self, j: DiversifierIndex) -> Result<(DiversifierIndex, PaymentAddress), ()> {
-        let (j, d_j) = match self.dk.diversifier(j) {
-            Ok(ret) => ret,
-            Err(()) => return Err(()),
-        };
+        let (j, d_j) = self.dk.diversifier(j)?;
         match self.fvk.vk.to_payment_address(d_j) {
             Some(addr) => Ok((j, addr)),
             None => Err(()),