lib-fs: Make sure fs-metawrap catches all write errors.

The full istream may not have been written in case ostream only partially
wrote the data (e.g. out of disk space?)

src/lib-fs/fs-metawrap.c

@@ -430,21 +430,22 @@ static int fs_metawrap_write_stream_finish(struct fs_file *_file, bool success)
 		i_stream_unref(&input2);
 	}
 	file->super_output = fs_write_stream(file->super);
-	if (o_stream_send_istream(file->super_output, input) >= 0)
-		ret = fs_write_stream_finish(file->super, &file->super_output);
-	else if (input->stream_errno != 0) {
+	(void)o_stream_send_istream(file->super_output, input);
+	if (input->stream_errno != 0) {
 		fs_set_error(_file->fs, "read(%s) failed: %s",
 			     i_stream_get_name(input),
 			     i_stream_get_error(input));
 		fs_write_stream_abort(file->super, &file->super_output);
 		ret = -1;
-	} else {
-		i_assert(file->super_output->stream_errno != 0);
+	} else if (file->super_output->stream_errno != 0) {
 		fs_set_error(_file->fs, "write(%s) failed: %s",
 			     o_stream_get_name(file->super_output),
 			     o_stream_get_error(file->super_output));
 		fs_write_stream_abort(file->super, &file->super_output);
 		ret = -1;
+	} else {
+		i_assert(i_stream_is_eof(input));
+		ret = fs_write_stream_finish(file->super, &file->super_output);
 	}
 	i_stream_unref(&input);
 	return ret;