[ffmpegthumbs] Remove the 1px border from thumbnails
Review Request #129923 - Created Feb. 5, 2017 and submitted
This is part of https://git.reviewboard.kde.org/r/129921/.
Returning DrawFrame in flags results in a 1px black and white border getting added to the thumbnail while returning None does not.
There is no reason why it should be adding a border.
Especially since this thumbnail creator generates images that could (and should IMO) be treated the same as thumbnails from, say, image files like wallpapers etc.