I had this same issue and found this post on the forum. I made the changes to the file as you suggested and now it works fine. Thanks!
By the way, in looking to change the string, I did notice that there was a slight difference in spacing in what needed to be replaced. Some places it appeared as
if ( $params->get('show_input_buy_now'
&& $media->informationFrom == 1)
and other places it appeared as
if ( $params->get('show_input_buy_now'
&& $media->informationFrom == 1 )
with an extra space after the 1.
This might not make a difference in the code, but if does affect a simple search and replace since if you search and replace the first string, you will miss the second one.