Fixed a crash on moving down the last field in the Symbol Properties dialog

eeschema/dialogs/dialog_edit_component_in_schematic.cpp

@@ -645,7 +645,7 @@ void DIALOG_EDIT_COMPONENT_IN_SCHEMATIC::OnMoveDown( wxCommandEvent& event )
 
     int i = m_grid->GetGridCursorRow();
 
-    if( i >= MANDATORY_FIELDS )
+    if( i >= MANDATORY_FIELDS && i < m_grid->GetNumberRows() - 1 )
     {
         SCH_FIELD tmp = m_fields->at( (unsigned) i );
         m_fields->erase( m_fields->begin() + i, m_fields->begin() + i + 1 );