Reset pending surface delta x and y on commit
Reset pending surface delta x and y on commit

The following sequence:
	wl_surface::attach(s, b, 1, 2)
	wl_surface::commit(s)
	wl_surface::commit(s)
would actually result in the surface getting moved by (2,4) as the
pending attach delta wasn't reset on commit, only by another attach.

This only shows up on single-buffered surfaces.

Signed-off-by: Daniel Stone <3d0f3b9ddcacec30c4008c5e030e6c13a478cb4f@fooishbar.org>

Fantu/compositor-spice,jonnylamb/weston,kwm81/weston,Gnurou/weston,xorgy/weston,sir-murray/weston,eyolfson/weston,kwm81/weston,mchalupa/weston,krezovic/weston,sir-murray/weston,krezovic/weston,xorgy/weston,Fantu/compositor-spice,udoprog/weston,giucam/weston,giucam/weston,mchalupa/weston,udoprog/weston,Fantu/compositor-spice,eyolfson/weston,Tarnyko/weston-xdg_surface_present,jonnylamb/weston,Tarnyko/weston-xdg_surface_present,Gnurou/weston