change assert to warning
change assert to warning

Summary: it's a pretty dangerous pitfall. the message shouldn't be limited to debug builds

Test Plan: build

Reviewers: vmrob

Reviewed By: vmrob

Subscribers: #engineering

Differential Revision: https://phabricator.btlive.tv/D1916

bittorrent/scraps,bittorrent/scraps,bittorrent/scraps,bittorrent/scraps