improve performance of commit-graph variant ever-so-slightly

Author: Byron

gix-revision/src/merge_base.rs

@@ -217,11 +217,10 @@ pub(crate) mod function {
         type Error = gix_object::decode::Error;
 
         fn try_from(commit: LazyCommit<'_, '_>) -> Result<Self, Self::Error> {
+            let (generation, timestamp) = commit.generation_and_timestamp()?;
             Ok(GenThenTime {
-                generation: commit
-                    .generation()
-                    .unwrap_or(gix_commitgraph::GENERATION_NUMBER_INFINITY),
-                time: commit.committer_timestamp()?,
+                generation: generation.unwrap_or(gix_commitgraph::GENERATION_NUMBER_INFINITY),
+                time: timestamp,
             })
         }
     }