Creating empty archive results in file_size and data_start being zero in SARC header

[davidzchen]

Steps to reproduce:

1. Create an empty directory
2. Run SARC-Tool on the empty directory to create an empty archive.
3. Inspect header

I wrote a tool (in a private repository) that dumps the headers and other metadata for a SARC archive, and here is what I got when running on an empty archive:

$ bazel build //tools:sarc-dump
$ bazel-bin/tools/sarc-dump oepd/sarc/testdata/empty-little-endian.sarc
SARC Archive: oepd/sarc/testdata/empty-little-endian.sarc

Endian: Little Endian

== SARC Header
magic:           53415243
header_size:     14
byte_order_mark: feff
file_size:       0
data_start:      0
version:         100
reserved:        0

== SFAT Header
magic:       53464154
header_size: c
nodes_count: 0
hash_key:    65

== SFNT Header
magic:       53464e54
header_size: 8
reserved:    0

-- File Names:

Is this a bug? IIUC, file_size should be the size of the entire archive, while data_start should be the offset from the beginning of the archive to where the file data starts (rather than the offset after the headers).

The zeldamodees/oead implementation seems to confirm this: https://github.com/zeldamods/oead/blob/b31e5bc96bab9ee7e84971c8f2ca34073d0263af/src/sarc.cpp#L331-L341