fix: propagate errors that are triggered when writing objects (#1678)

Previously it was assumed that writing objects could never fail unless
there isn't enough memory to do so. However, it turns out that
some last-minute validation can always be triggered and prevent an object
to be written.

Now that error is propagated instead.

Author: Byron

gix/src/repository/object.rs

@@ -164,7 +164,9 @@ impl crate::Repository {
     /// we avoid writing duplicate objects using slow disks that will eventually have to be garbage collected.
     pub fn write_object(&self, object: impl gix_object::WriteTo) -> Result<Id<'_>, object::write::Error> {
         let mut buf = self.empty_reusable_buffer();
-        object.write_to(buf.deref_mut()).expect("write to memory works");
+        object
+            .write_to(buf.deref_mut())
+            .map_err(|err| Box::new(err) as Box<dyn std::error::Error + Send + Sync + 'static>)?;
 
         self.write_object_inner(&buf, object.kind())
     }

gix/tests/gix/repository/object.rs

@@ -254,7 +254,7 @@ mod write_object {
         };
         assert_eq!(
             repo.write_object(commit).unwrap_err().to_string(),
-            "TBD",
+            "Signature name or email must not contain '<', '>' or \\n",
             "the actor is invalid so triggers an error when persisting it"
         );
         Ok(())