branch: delete branch description if it's empty

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/branch.c

@@ -700,7 +700,7 @@ static int edit_branch_description(const char *branch_name)
 	stripspace(&buf, 1);
 
 	strbuf_addf(&name, "branch.%s.description", branch_name);
-	status = git_config_set(name.buf, buf.buf);
+	status = git_config_set(name.buf, buf.len ? buf.buf : NULL);
 	strbuf_release(&name);
 	strbuf_release(&buf);