gldeinterlace: does nothing when scaling

Submitted by Tim Müller @tpm

Link to original bug (#767388)

Description

gst-launch-1.0 uridecodebin uri=https://people.freedesktop.org/~tpm/samples/bbcnews.m2t ! videoconvert ! glupload ! gldeinterlace ! gldownload ! videoconvert ! videoscale ! ximagesink

This appears to do some deinterlacing when the video window is the default size, but when maximising the window it looks like no deinterlacing is done.