Populate bucket ID with file ID when local-only is enabled

Since the B2 API requires the bucket ID to be used for single-chunk
downloads and the file ID to be used for multi-chunk uploads, both
should be populated with the same value (the file ID/name) when
local-only mode is enabled. This way the library can be used the same
with or without access to an actual B2 bucket.

list_files.go

@@ -146,6 +146,7 @@ func listLocalFiles(path string) (FileList, error) {
 		fileList = append(fileList, FileListItem{
 			FileName:      name,
 			FileID:        name,
+			BucketID:      name,
 			ContentLength: int(stat.Size()),
 		})
 	}

upload_file.go

@@ -196,7 +196,8 @@ func uploadLocalFile(
 
 	return File{
 		FileID:        filename,
-		ContentLength: len(contents),
+		BucketID:      filename,
 		FileName:      filename,
+		ContentLength: len(contents),
 	}, nil
 }

upload_large_file.go

@@ -400,6 +400,7 @@ func finishLargeLocalFile(id string, path string) (LargeFile, error) {
 	return LargeFile{
 		FileID:        id,
 		FileName:      id,
+		BucketID:      id,
 		ContentLength: int(stat.Size()),
 	}, nil
 }