fix fluid diff change

Summary: when we had a change that had new data and uncommitted changes the colspan could get off. make sure to only decrement the colspan if we are actually on a new line

Test Plan: http://phabricator.dev/rP1a3bf098ae4ab4f8add4af744a6b93a257851fb0 now looks good on Firefox

Reviewers: vrana, epriestley

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T2005

Differential Revision: https://secure.phabricator.com/D4109