Older popler (SLE11) does not have this header yet.
With the code simply if the header not found define version to oldest
possible working candidate and also raise the .pc check to the same.

Change-Id: I039c879879188fe2eb90cd119b80a1d6354a6a9c
Reviewed-on: https://gerrit.libreoffice.org/15339Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>