always malloc to avoid potential crash in putenv.

Reference: /n/atom/patch/applied2013/envsetupmal
Date: Wed Aug 21 01:37:27 CES 2013
Signed-off-by: quanstro@quanstro.net

--- /sys/src/ape/lib/ap/plan9/_envsetup.c	Wed Aug 21 01:37:01 2013
+++ /sys/src/ape/lib/ap/plan9/_envsetup.c	Wed Aug 21 01:37:01 2013
@@ -45,8 +45,8 @@
 	cnt = 0;
 	dfd = _OPEN("/env", 0);
 	if(dfd < 0) {
-		static char **emptyenvp = 0;
-		environ = emptyenvp;
+		environ = malloc(sizeof(char**));
+		*environ = NULL;
 		return;
 	}
 	ps = p = malloc(Envhunk);