vcl::ITiledRenderable: getTextSelection() can be pure virtual now

Change-Id: Ifb33ee9a70afeccc01f45996b2953fcd5f3700cc
Reviewed-on: https://gerrit.libreoffice.org/16906Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Jenkins <ci@libreoffice.org>

include/vcl/ITiledRenderable.hxx

@@ -126,7 +126,7 @@ public:
      *
      * @see lok::Document::getTextSelection().
      */
-    virtual OString getTextSelection(const char* /*pMimeType*/, OString& /*rUsedMimeType*/) { return OString(); }
+    virtual OString getTextSelection(const char* pMimeType, OString& rUsedMimeType) = 0;
 
     /**
      * Adjusts the graphic selection.