tal/path: fix unset vars in error paths.

Compiling with optimization FTW.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
ccan: Fix calling memset with zero length parameter

Signed-off-by: Volker Lendecke <vl@samba.org>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>