fetch: improve --link handling

Handle file: URLs correctly, and don't do linkat() syscall if
it is a remote repository.

Also account the file size to progress always.

src/app_fetch.c

@@ -191,10 +191,10 @@ static int fetch_package(struct apk_database *db, const char *match, struct apk_
 		os = apk_ostream_to_fd(STDOUT_FILENO);
 	} else {
 		if ((ctx->flags & FETCH_LINK) && urlfd >= 0) {
-			if (linkat(urlfd, url,
-				   ctx->outdir_fd, filename,
-				   AT_SYMLINK_FOLLOW) == 0)
-				return 0;
+			const char *urlfile = apk_url_local_file(url);
+			if (urlfile &&
+			    linkat(urlfd, urlfile, ctx->outdir_fd, filename, AT_SYMLINK_FOLLOW) == 0)
+				goto done;
 		}
 		os = apk_ostream_to_file(ctx->outdir_fd, filename, 0644);
 		if (IS_ERR(os)) {
@@ -214,13 +214,13 @@ static int fetch_package(struct apk_database *db, const char *match, struct apk_
 	apk_istream_close(is);
 	r = apk_ostream_close(os);
 	if (r) goto err;
-
-	ctx->done += pkg->size;
-	return 0;
+	goto done;
 
 err:
 	apk_err(out, PKG_VER_FMT ": %s", PKG_VER_PRINTF(pkg), apk_error_str(r));
 	ctx->errors++;
+done:
+	ctx->done += pkg->size;
 	return 0;
 }