Initialize nfds fields of new file structures.

Fixes possible crash when a new file structure is added in
the time-out processing code-path.

sndiod/file.c

@@ -235,6 +235,7 @@ file_new(struct fileops *ops, void *arg, char *name, unsigned int nfds)
 	}
 	f = xmalloc(sizeof(struct file));
 	f->max_nfds = nfds;
+	f->nfds = 0;
 	f->ops = ops;
 	f->arg = arg;
 	f->name = name;