Only add row separator between rows.

Fixes https://gitlab.com/kicad/code/kicad/-/issues/20494

(cherry picked from commit 4f83674b62)

common/grid_tricks.cpp

@@ -854,6 +854,9 @@ void GRID_TRICKS::cutcopy( bool doCopy, bool doDelete )
     // fill txt with a format that is compatible with most spreadsheets
     for( int row = m_sel_row_start;  row < m_sel_row_start + m_sel_row_count;  ++row )
     {
+        if( !txt.IsEmpty() )
+            txt += ROW_SEP;
+
         for( int col = m_sel_col_start;  col < m_sel_col_start + m_sel_col_count; ++col )
         {
             if( !m_grid->IsColShown( col ) )
@@ -872,8 +875,6 @@ void GRID_TRICKS::cutcopy( bool doCopy, bool doDelete )
                     tbl->SetValue( row, col, wxEmptyString );
             }
         }
-
-        txt += ROW_SEP;
     }
 
     if( doCopy )