fix an issue in example program

example.c

@@ -13,6 +13,7 @@ static inline bool acg_flush(struct acg_stream* s) {
   if (s->cursor_bits < 8U) {
     return false;
   }
+
   FILE** fp = (void*) &s->udata;
   if (NULL == *fp) {
     *fp = fopen("log.acg", "wb");
@@ -23,6 +24,9 @@ static inline bool acg_flush(struct acg_stream* s) {
   if (1U != fwrite(s->buffer, s->cursor_bits/8U, 1U, *fp)) {
     return false;
   }
+  memset(s->buffer, 0U, (s->cursor_bits+7U)/8U);
+  s->cursor_bits = 0;
+
   if (0U != fflush(*fp)) {
     return false;
   }