tdf#97235: Protect reset_view when called with no tile buffer initialized

This can happen when no document has been loaded yet.

Change-Id: Ib9c18e22b6c344528d05eb781bf9b3052060089a

libreofficekit/source/gtk/lokdocview.cxx

@@ -2825,6 +2825,8 @@ SAL_DLLPUBLIC_EXPORT void
 lok_doc_view_reset_view(LOKDocView* pDocView)
 {
     LOKDocViewPrivate& priv = getPrivate(pDocView);
+
+    if (priv->m_pTileBuffer != nullptr)
         priv->m_pTileBuffer->resetAllTiles();
     priv->m_nLoadProgress = 0.0;