Fix for one of the filter tests.

Occasionally characters are assembled via multiple calls to Characters() esp
when the content includes encoded characters and/or XML comments.

Change-Id: I1b6d1e7490350add77388330b183504c24deaab4

sc/source/filter/xml/celltextparacontext.cxx

@@ -38,7 +38,7 @@ void ScXMLCellTextParaContext::EndElement()
 
 void ScXMLCellTextParaContext::Characters(const OUString& rChars)
 {
-    maContent = rChars;
+    maContent += rChars;
 }
 
 SvXMLImportContext* ScXMLCellTextParaContext::CreateChildContext(