Oversight/Bug: Picking a filesize larger then intended causes upped bitrate (--web)

[theo-croft]

Normally this does not seem that bad though this becomes a BIT of a problem when you end up with a 13 second 90mb file (total bitrate of 54177 kbps) which can often lead to buffering on non speedy internet. or cause excess data consumption

Steps to reproduce:

1. set target size over original file size
2. (optional) shorten inital video length

It appears if there is additonal space that can be filled, the encoder tries to up the bitrate, the solution would be to either not require a target file size, or input the same target file size as the video.