httpd: nul terminate buffer in readfile
 [rsc] --rw-rw-r-- M 836007 glenda sys 2403 Apr 14 10:01 sys/src/cmd/ip/httpd/authorize.c
	/n/sourcesdump/2006/0414/plan9/sys/src/cmd/ip/httpd/authorize.c:111,115 - 
	/n/sourcesdump/2006/0415/plan9/sys/src/cmd/ip/httpd/authorize.c:111,116
	  		free(buf);
	  		return nil;
	  	}
	+ 	buf[n] = '\0';
	  	return buf;
	  }