FILE's closed in ERR state are not marked as CLOSED and thus cannot be reused.

Reference: /n/sources/patch/applied/stdio.file.leak
Date: Wed Dec  7 16:52:22 CET 2005

--- /sys/src/ape/lib/ap/stdio/sclose.c	Wed Dec  7 16:51:10 2005
+++ /sys/src/ape/lib/ap/stdio/sclose.c	Wed Dec  7 16:51:07 2005
@@ -9,6 +9,7 @@
 	default:	/* ERR CLOSED */
 		if(f->buf && f->flags&BALLOC)
 			free(f->buf);
+		f->state=CLOSED;
 		f->flags=0;
 		return NULL;
 	case OPEN: