die() in .tmpl file should not be silently ignored.

die() in .tmpl file should not be silently ignored.

call to die() in perl templates is currently ignored.
any error printed by die() commad appears in template
output.

In order to make sure die() terminates processing we
must ensure we emite `undef` value. This is ensured
by adding a `BROKEN` callback to `fill_in()` Template
method. The callback must return undef to stop processing.

Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/26064)