lib.sh: set -u -e in err()

Some parts of lbmk set +u +e, to be reset later on
under normal conditions upon exit. We must ensure
such level of integrity in err() as well.

Signed-off-by: Leah Rowe <leah@libreboot.org>

include/lib.sh

@@ -176,6 +176,8 @@ x_()
 
 err()
 {
+	set -u -e
+
 	xbmk_err_val=0
 	real_err="" && [ -n "${xbmk_err+x}" ] && real_err="$xbmk_err"