compositor: improve viewport source validity check

If client changes the buffer transform or size and re-commit the surface
before surface dirtys buffer (weston_surface_attach), the viewport
source validity check may fail. Because the width_from_buffer and
height_from_buffer cannot be updated based on new buffer transform.

Therefore, add the situation of size dirty (WESTON_SURFACE_DIRTY_SIZE) to
source validity check, width_from_buffer and height_from_buffer can be
updated in time when the buffer transform and scale change.

Signed-off-by: Chao Guo <chao.guo@nxp.com>