e29bde subr.pkg/pkg_configure_patch.subr: don't apply patches if "${PKG_BASE_DIR}/${PKG_SUBDIR}/srcprep.sh" exists.

Authored and Committed by lalbornoz a month ago
    subr.pkg/pkg_configure_patch.subr: don't apply patches if "${PKG_BASE_DIR}/${PKG_SUBDIR}/srcprep.sh" exists.