main/zlib: support newer abuild

which will move /lib/*.a to -dev subpackage for us

main/zlib/APKBUILD

@@ -34,7 +34,10 @@ package() {
 dev() {
 	default_dev
 	mkdir -p "$subpkgdir"/lib
-	mv "$pkgdir"/lib/libz.a "$subpkgdir"/lib/libz.a
+	# newer abuild might do this for us
+	if [ -f "$pkgdir"/libz.a ]; then
+		mv "$pkgdir"/lib/libz.a "$subpkgdir"/lib/libz.a
+	fi
 }
 
 md5sums="44d667c142d7cda120332623eab69f40  zlib-1.2.8.tar.gz"