kde-apps/step: Fix configure with USE=-nls

Make missing 'po' subdirectory non-fatal.

Reported-by: Jaak Ristioja <jaak@ristioja.ee>
Gentoo-bug: 618556

Package-Manager: Portage-2.3.5, Repoman-2.3.1

kde-apps/step/step-17.04.1.ebuild

@@ -49,6 +49,10 @@ DEPEND="${RDEPEND}
 src_prepare() {
 	kde5_src_prepare
 
+	# FIXME: Should be upstream in 17.04.2
+	sed -e 's/add_subdirectory( *po *)/ecm_optional_add_subdirectory(po)/' \
+		-i CMakeLists.txt || die
+
 	# FIXME: Drop duplicate upstream
 	sed -e '/find_package.*Xml Test/ s/^/#/' \
 		-i stepcore/CMakeLists.txt || die