Use the now-idiomatic option? syntax

This works in Rust now:

    foo?;

as a replacement for:

    if foo.is_none() {
        return None;
    }

It's similar to ? for error handling and can only be used in functions
that return an Option.

The instance of this in a macro caused the problem to be reported a
lot of time, once per time the macro was used, but luckily it can
could be fixed in only one place. Magic!

Found by clippy lint question_mark:
https://rust-lang.github.io/rust-clippy/master/index.html#question_mark

1 files changed, 2 insertions, 8 deletions

diff --git a/openpgp/src/cert/amalgamation/key/iter.rs b/openpgp/src/cert/amalgamation/key/iter.rs
index f23b1a15..370a4e43 100644
--- a/openpgp/src/cert/amalgamation/key/iter.rs
+++ b/openpgp/src/cert/amalgamation/key/iter.rs
@@ -143,10 +143,7 @@ impl<'a, P, R> KeyAmalgamationIter<'a, P, R>
         tracer!(false, "KeyAmalgamationIter::next", 0);
         t!("KeyAmalgamationIter: {:?}", self);
 
-        if self.cert.is_none() {
-            return None;
-        }
-        let cert = self.cert.unwrap();
+        let cert = self.cert?;
 
         loop {
             let ka : ErasedKeyAmalgamation<key::PublicParts>
@@ -742,10 +739,7 @@ impl<'a, P, R> ValidKeyAmalgamationIter<'a, P, R>
         tracer!(false, "ValidKeyAmalgamationIter::next", 0);
         t!("ValidKeyAmalgamationIter: {:?}", self);
 
-        if self.cert.is_none() {
-            return None;
-        }
-        let cert = self.cert.unwrap();
+        let cert = self.cert?;
 
         if let Some(flags) = self.flags.as_ref() {
             if flags.is_empty() {