The horrible SvxAutoCorrect::AutoCorrect() inserts the character into
the document half-way through, and then _expects_ this inserted
character to show up in its rTxt parameter.  This broke in Writer when
SwTxtNode::m_Text was converted to OUString, because now a
temporary String copy is created.  Work around this disaster area for
now.

(regression from 0295c8a3)

Change-Id: I1cb11a20cb0c2577036176e605426105631f3311