Don't create a final empty packfile in fast-import.

If the last packfile is going to be empty (has 0 objects) then it
shouldn't be kept after the import has terminated, as there is no
point to the packfile.  So rather than hashing it and making the
index file, just delete the packfile.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

fast-import.c

@@ -713,17 +713,23 @@ static void end_packfile()
 {
 	struct packed_git *old_p = pack_data, *new_p;
 
-	fixup_header_footer();
-	write_index(idx_name);
+	if (object_count) {
+		fixup_header_footer();
+		write_index(idx_name);
 
-	/* Register the packfile with core git's machinary. */
-	new_p = add_packed_git(idx_name, strlen(idx_name), 1);
-	if (!new_p)
-		die("core git rejected index %s", idx_name);
-	new_p->windows = old_p->windows;
-	new_p->pack_fd = old_p->pack_fd;
-	all_packs[pack_id++] = new_p;
-	install_packed_git(new_p);
+		/* Register the packfile with core git's machinary. */
+		new_p = add_packed_git(idx_name, strlen(idx_name), 1);
+		if (!new_p)
+			die("core git rejected index %s", idx_name);
+		new_p->windows = old_p->windows;
+		new_p->pack_fd = old_p->pack_fd;
+		all_packs[pack_id++] = new_p;
+		install_packed_git(new_p);
+	}
+	else {
+		close(pack_fd);
+		unlink(old_p->pack_name);
+	}
 	free(old_p);
 	free(idx_name);