glimagesink: always send a reconfigure event when starting

Submitted by Julien Isorce @cap

Link to original bug (#755454)

Description

Not sure for how long this problem is there, but it always resize the window to 1x1 and then resize to the desired size.
To from 0x0 to 1x1 does not triggered a reconfigure event. As initial values are 0x0.
But change from 1x1 to 320x240 triggers a reconfigure event, Which potentially deactivate /reactive upstream pools which adds unnecessary delays.

Patch follows.