maildir: Don't crash with zlib plugin when saving is aborted

The ostream can be finished even if the saving had already failed. It gets
deleted anyway.

Fixes:
Panic: file ostream-zlib.c: line 37 (o_stream_zlib_close): assertion failed: (zstream->ostream.finished || zstream->ostream.ostream.stream_errno != 0 || zstream->ostream.error_handling_disabled)

src/lib-storage/index/maildir/maildir-save.c

@@ -510,7 +510,7 @@ static int maildir_save_finish_real(struct mail_save_context *_ctx)
 	}
 
 	path = t_strconcat(ctx->tmpdir, "/", ctx->file_last->tmp_name, NULL);
-	if (!ctx->failed && o_stream_finish(_ctx->data.output) < 0) {
+	if (o_stream_finish(_ctx->data.output) < 0) {
 		if (!mail_storage_set_error_from_errno(storage)) {
 			mail_set_critical(_ctx->dest_mail,
 				"write(%s) failed: %s", path,