Overflow in storage.tsdb.max-block-duration

[SuperQ]

Bug Report

What did you do?

Set --storage.tsdb.retention=500y

What did you expect to see?

storage.tsdb.max-block-duration in /flags would be "50y"

What did you see instead? Under which circumstances?

storage.tsdb.max-block-duration returns -267874407370ms

Environment

• System information:

Linux 4.18.0-13-generic x86_64

• Prometheus version:

prometheus, version 2.6.0 (branch: HEAD, revision: dbd1d58c894775c0788470944b818cc724f550fb)
  build user:       root@bf5760470f13
  build date:       20181217-15:14:46
  go version:       go1.11.3