931: fix rollback display logic for the diffing page
931: fix rollback display logic for the diffing page

Now it matches the logic for when we show the rollback button on the
page for the subtitle version.

wevoice/wesub,ujdhesa/unisubs,wevoice/wesub,wevoice/wesub,ofer43211/unisubs,ReachingOut/unisubs,ofer43211/unisubs,pculture/unisubs,pculture/unisubs,wevoice/wesub,norayr/unisubs,ReachingOut/unisubs,norayr/unisubs,eloquence/unisubs,ujdhesa/unisubs,norayr/unisubs,ujdhesa/unisubs,pculture/unisubs,ofer43211/unisubs,eloquence/unisubs,norayr/unisubs,ReachingOut/unisubs,eloquence/unisubs,ujdhesa/unisubs,pculture/unisubs,eloquence/unisubs,ofer43211/unisubs,ReachingOut/unisubs