rust-revlog: split logic for `rawdata` to prepare for `UncheckedRevision` use

In the next changeset, we will change the logic to use `UncheckedRevision`
in the non-general delta case. The general delta case will use the "checked"
path since `base_rev_or_base_of_delta_chain` will be checked.

rust/hg-core/src/revlog/mod.rs

@@ -537,13 +537,14 b" impl<'revlog> RevlogEntry<'revlog> {"
         // [_chaininfo] and in [index_deltachain].
         let uses_generaldelta = self.revlog.index.uses_generaldelta();
         while let Some(base_rev) = entry.base_rev_or_base_of_delta_chain {
-            let base_rev = if uses_generaldelta {
-                base_rev
+            entry = if uses_generaldelta {
+                delta_chain.push(entry);
+                self.revlog.get_entry_internal(base_rev)?
             } else {
-                entry.rev - 1
+                let base_rev = entry.rev - 1;
+                delta_chain.push(entry);
+                self.revlog.get_entry_internal(base_rev)?
             };
-            delta_chain.push(entry);
-            entry = self.revlog.get_entry_internal(base_rev)?;
         }
 
         let data = if delta_chain.is_empty() {