spatial svc: set window_size to 15
spatial svc: set window_size to 15

Static analysis does not recognize that output_rc_stat guards
the usage of window_size. Clears this warning:
The right operand of '>' is a garbage value
if (frame_cnt > (unsigned int)rc.window_size) {

set_rate_control_stats sets window_size to 15. Zeroing it
just introduces another static analysis warning.

Change-Id: Ieee7b81a385f986e42189101cfa39279e519b368

webmproject/libvpx,ShiftMediaProject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx