videoconvert: Setting height to 1 freezes output in some cases

Submitted by Dimitrios Katsaros

Link to original bug (#748179)

Description

If a pipleline is created like the following:

gst-launch-1.0 v4l2src device=/dev/video0 ! video/x-raw, height=1 ! videoconvert ! ximagesink

The output of the ximagesink is frozen after the first frame. Changing the ximagesink with another sink, e.g. glimagesink works normally