lib: Don't set ostream buffer as blocking

src/lib/ostream-buffer.c

@@ -59,7 +59,9 @@ struct ostream *o_stream_create_buffer(buffer_t *buf)
 	struct ostream *output;
 
 	bstream = i_new(struct buffer_ostream, 1);
-	bstream->ostream.ostream.blocking = TRUE;
+	/* we don't set buffer as blocking, because if max_buffer_size is
+	   changed it can get truncated. this is used in various places in
+	   unit tests. */
 	bstream->ostream.max_buffer_size = (size_t)-1;
 	bstream->ostream.seek = o_stream_buffer_seek;
 	bstream->ostream.sendv = o_stream_buffer_sendv;