fdo#45394 fix RTF import of tables with empty first row

Additionally the table should be at the start of the document to trigger
this bug.

writerfilter/source/rtftok/rtfdocumentimpl.cxx

@@ -1392,6 +1392,7 @@ int RTFDocumentImpl::dispatchSymbol(RTFKeyword nKeyword)
         case RTF_CELL:
         case RTF_NESTCELL:
             {
+                checkFirstRun();
                 if (m_bNeedPap)
                 {
                     // There were no runs in the cell, so we need to send paragraph and character properties here.