Fix oplog truncation

Author: lalinsky

src/Index.zig

@@ -215,6 +215,10 @@ fn doCheckpoint(self: *Self) !bool {
 
     try self.updateManifestFile(file_segments_update.segments.value);
 
+    defer self.oplog.truncate(target.value.info.getLastCommitId()) catch |err| {
+        log.warn("failed to truncate oplog: {}", .{err});
+    };
+
     // commit updated lists
 
     self.segments_lock.lock();

src/Oplog.zig

@@ -187,10 +187,11 @@ fn truncateNoLock(self: *Self, commit_id: u64) !void {
     var buf: [file_name_size]u8 = undefined;
     while (pos > 0) {
         pos -= 1;
-        const file_info = self.files.orderedRemove(pos);
+        const file_info = self.files.items[pos];
         const file_name = try generateFileName(&buf, file_info.id);
         log.info("deleting oplog file {s}", .{file_name});
         try self.dir.deleteFile(file_name);
+        _ = self.files.orderedRemove(pos);
     }
 }