wayland/surface: Don't save uninitialized size

wayland/surface: Don't save uninitialized size

GdkSurface's are initialized to have the size 1x1, as otherwise we'd
receive an X11 error, would a corresponding X11 window be created.

This confuses the "saved size" mechanisms in the Wayland backend, as
treats 0 as uninitialized, and not 1.

Fix this simply not saving size that if it's smaller or equal than 1.