Another attempt, whoever has written this apparently didn't consider
the possibility of recursion at all, and this still feels a bit hackish.
Writerfilter keeps just one oox::shape::ShapeContextHandler object during
the entire time of parsing the document, because e.g. <v:shapetype> needs
to be reachable even across VML block (see sw testcases for bnc#705956).
This however presents a problem when VML contains <w:txbxContent> which
contains another VML, as this code previously just took whatever has been
read and returned it to writerfilter, and it broke with recursion.
So now try to mark recursion entry and returns the right shape.
Related to 36c12c246d886b2d96d7a2d4d0c250db9d925c74 and the previous
commits it reverted.
Change-Id: I949a6b52ec7540aa59b047c7b6e908b10fb3bdc1
886e29cff7