Whenever the surface is resized before the stream is negotiated, we endup
with an assertion in libgstvideo.
gst_video_center_rect: assertion 'src->h != 0' failed
This fixes it, by following the style aready in place, which is to ensure
surfaces have a minimum size of 1x1.
Fixes#1139
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/3467>