fix 0-extension bug

Reference: /n/atom/patch/applied/srvold9pmask
Date: Sun Aug 16 00:13:24 CES 2015
Signed-off-by: quanstro@quanstro.net

--- /sys/src/cmd/srvold9p/9p1lib.c	Sun Aug 16 00:13:25 2015
+++ /sys/src/cmd/srvold9p/9p1lib.c	Sun Aug 16 00:13:26 2015
@@ -355,7 +355,7 @@
 	STRING(uid, NAMEREC);
 	STRING(gid, NAMEREC);
 
-	q = f->qid.path & ~0x80000000;
+	q = f->qid.path & ~(uvlong)0x80000000;
 	if(f->qid.type & QTDIR)
 		q |= 0x80000000;
 	VLONG(q);
@@ -582,7 +582,7 @@
 	p += NAMEREC;
 
 	LONG(qid.path);
-	f->qid.path &= ~0x80000000;
+	f->qid.path &= ~(uvlong)0x80000000;
 
 	LONG(qid.vers);
 	LONG(mode);