gstglwindow_x11: fix resize

gstglwindow_x11: fix resize

This patch was taken from #629#note_178766, the comment made
at the time was:

The root issue is a mismatch between the initialization of render_rect
in GstGLWindowX11Private and what's expected in the draw_cb function.
Because render_rect is not explicitly initialized to a width and height
of -1 (unlike gstglwindow_wayland_egl.c which does initialize to -1),
the less-than check for explicitly-set render_rect at gstglwindow_x11.c:453-454
always fails, even when the parent_win has been set and the render rectangle
has never been set.

Maybe this came from copying the similar check in the wayland code? Regardless,
I think the correct inequality should be '<= 0' (on both lines).

Alternatively initialization could be changed, but other sinks, e.g.
xvimagesink don't appear to use -1 to mean "unset" render_rect this way.

The issue can be reproduced by running the example in
tests/examples/gl/qt/videooverlay/ on X11, and resizing the output
window

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-base/-/merge_requests/701>