commit: use read_header

The `Odb::reader` method states:

    Note that most backends do not support streaming reads because
    they store their objects as compressed/delta’ed blobs. If the
    backend does not support streaming reads, use the read method
    instead.

This can lead to objects not being found when verifying for
commits. Instead use `read_header` to determine the `ObjectType` of
the `Oid`.

Signed-off-by: Fintan Halpenny <fintan.halpenny@gmail.com>
X-Clacks-Overhead: GNU Terry Pratchett

radicle-git-ext/src/commit.rs

@@ -149,8 +149,8 @@ impl Commit {
 fn verify_object(odb: &git2::Odb, oid: &Oid, expected: ObjectType) -> Result<(), error::Write> {
     use git2::{Error, ErrorClass, ErrorCode};
 
-    let (_, _, kind) = odb
-        .reader(*oid)
+    let (_, kind) = odb
+        .read_header(*oid)
         .map_err(|err| error::Write::OdbRead { oid: *oid, err })?;
     if kind != expected {
         Err(error::Write::NotCommit {