...as the SwTextBlocks ctor internally calls SwDOCXReader::MakeEntries ->
BeginPutDoc which wants to open the document read-write.  That would fail if
SRCDIR is a read-only tree.

Change-Id: I433b80bcec53c8ca4282d1f45c941153a4064eb9
Reviewed-on: https://gerrit.libreoffice.org/52053Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>