debian-package.bbclass: check patchs only if DEBIAN_QUILT_PATCHES is empty
debian-package.bbclass: check patchs only if DEBIAN_QUILT_PATCHES is empty

If DEBIAN_QUILT_PATCHES is the default path or another custom path
specified by users, no need to confirm if series and other patches
exist or not.

Signed-off-by: Kazuhiro Hayashi <d6ab13038406a238a56011921c4eda80a48396fd@toshiba.co.jp>

meta-debian/meta-debian,meta-debian/meta-debian,meta-debian/meta-debian,meta-debian/meta-debian,meta-debian/meta-debian,meta-debian/meta-debian