Curling a file with a negative mtime

curl-test.shell

$ touch -t 196508231405.14 ./test.tgz"

$ stat ./test.tgz
  File: ‘test.tgz’
  Size: 6012            Blocks: 16         IO Block: 4096   regular file
Device: 900h/2304d      Inode: 127402426   Links: 1
Access: (0644/-rw-r--r--)  Uid: ( 1000/  ubuntu)   Gid: ( 1000/  ubuntu)
Access: 1965-08-23 14:05:14.000000000 +0000
Modify: 1965-08-23 14:05:14.000000000 +0000
Change: 2016-07-06 17:35:26.871223783 +0000
 Birth: -

$ curl -v localhost/test.tgz 1> /dev/null
 < HTTP/1.1 200 OK
....
< Last-Modified: Mon, 01 Jul 438498963 21:05:30 GMT
< Connection: keep-alive
< ETag: "-8320de6-177c"
....
$ curl -v -H 'if-none-match: "-8320de6-177c"' localhost/test.tgz 1>/dev/null
< HTTP/1.1 304 Not Modified
....
< Last-Modified: Mon, 01 Jul 438498963 21:05:30 GMT
< Connection: keep-alive
< ETag: "-8320de6-177c"
< Expires: Wed, 06 Jul 2016 23:40:19 GMT
< Cache-Control: max-age=21600
< Access-Control-Allow-Origin: *
  0     0    0     0    0     0      0      0 --:--:--  0:00:22 --:--:--     0