common: fix build error of used uninitialized
common: fix build error of used uninitialized

  CC     sw_canvas.lo
cc1: warnings being treated as errors
../common/sw_canvas.c: In function 'canvas_draw_text':
../common/sw_canvas.c:1037:16: error: 'pos.x' may be used uninitialized in this function
../common/sw_canvas.c:1037:16: error: 'pos.y' may be used uninitialized in this function
make[4]: *** [sw_canvas.lo] Error 1

Fantu/spice-gtk,guodong/spice-gtk,guodong/spice-gtk,dezelin/spice-gtk,dezelin/spice-gtk,flexVDI/spice-gtk,elmarco/spice-gtk,Fantu/spice-gtk,SPICE/spice-gtk,freedesktop-unofficial-mirror/spice__spice-gtk,Fantu/spice-gtk,freedesktop-unofficial-mirror/spice__spice-gtk,mathslinux/spice-gtk,flexVDI/spice-gtk,mathslinux/spice-gtk,guodong/spice-gtk,dezelin/spice-gtk,elmarco/spice-gtk,fgouget/spice-gtk,fgouget/spice-gtk,SPICE/spice-gtk,mathslinux/spice-gtk,elmarco/spice-gtk,freedesktop-unofficial-mirror/spice__spice-gtk,fgouget/spice-gtk,mathslinux/spice-gtk,SPICE/spice-gtk,Fantu/spice-gtk,elmarco/spice-gtk,dezelin/spice-gtk,guodong/spice-gtk,freedesktop-unofficial-mirror/spice__spice-gtk,SPICE/spice-gtk