Seoul fonts have broken GSUB table

```
$ ttx -o - -t GSUB seoulhangang/SeoulHangang-Light.ttf
Dumping "seoulhangang/SeoulHangang-Light.ttf" to "-"...

ERROR: An exception occurred during the decompilation of the 'GSUB' table
Traceback (most recent call last):
File "/usr/local/lib/python3.9/site-packages/fontTools/ttLib/ttFont.py", line 395, in _readTable
table.decompile(data, self)
File "/usr/local/lib/python3.9/site-packages/fontTools/ttLib/tables/otBase.py", line 41, in decompile
self.table.decompile(reader, font)
File "/usr/local/lib/python3.9/site-packages/fontTools/ttLib/tables/otBase.py", line 673, in decompile
table[conv.name] = conv.read(reader, font, table)
File "/usr/local/lib/python3.9/site-packages/fontTools/ttLib/tables/otConverters.py", line 432, in read
value = reader.readLong()
File "/usr/local/lib/python3.9/site-packages/fontTools/ttLib/tables/otBase.py", line 166, in readLong
return self.readValue("i", staticSize=4)
File "/usr/local/lib/python3.9/site-packages/fontTools/ttLib/tables/otBase.py", line 144, in readValue
value, = struct.unpack(f">{typecode}", self.data[pos:newpos])
struct.error: ('unpack requires a buffer of 4 bytes', 'Version')
Dumping 'GSUB' table...

```

The GSUB table is zero bytes. Same is true of SeoulHangang-Medium.ttf (but curiously not Bold/ExtraBold) as well as seoulnamsan/SeoulNamsan-Bold.ttf, seoulnamsan/SeoulNamsan-Medium.ttf, seoulnamsan/SeoulNamsan-Light.ttf.