[ing] added condition to verify the page before calling get_isin_code()

Several bugs occurred in production with NoneType has no attribute
get_isin_code(), probably because the investment URL does not work or
because some IPs are still blocked. In case the page did not load
properly, the "if self.detailfonds.is_here()" before calling get_isin_code() avoids
bugs during life insurance accounts synchronisation.