added gu_buf_flush in seq.c which removes all elements from a buffer

src/runtime/c/gu/seq.c

@@ -150,6 +150,12 @@ gu_buf_trim(GuBuf* buf)
 	return gu_buf_trim_n(buf, 1);
 }
 
+void
+gu_buf_flush(GuBuf* buf)
+{
+	gu_buf_set_length(buf, 0);
+}
+
 void
 gu_buf_pop_n(GuBuf* buf, size_t n_elems, void* data_out)
 {