core: added GRL_CORE_ERROR_OPERATION_CANCELLED
core: added GRL_CORE_ERROR_OPERATION_CANCELLED

Signed-off-by: Juan A. Suarez Romero <af79b5692270b306571bb1d8bbe0285ae3ac93d9@igalia.com>

grilofw/grilo,jasuarez/grilo,MathieuDuponchelle/grilo,kyoushuu/grilo,grilofw/grilo,GNOME/grilo,MathieuDuponchelle/grilo,GNOME/grilo,kyoushuu/grilo,kyoushuu/grilo,MathieuDuponchelle/grilo,grilofw/grilo,jasuarez/grilo,jasuarez/grilo,kyoushuu/grilo