(xml-lite-get-context): Allow stopping even with an empty context.

(xml-lite-get-context): Allow stopping even with an empty context.
Don't save excursion any more.  Ignore end-tags in sgml-empty-tags.
Don't complain about unmatched start-tags in sgml-unclosed-tags.
(xml-lite-get-context, xml-lite-calculate-indent)
(xml-lite-insert-end-tag): Save excursion around xml-lite-get-context.
(xml-lite-indent-line): Use back-to-indentation.