Fixes LineItem#update_price_from_modifier when currency specified and variant doesn't have a price in this currency
Fixes LineItem#update_price_from_modifier when currency specified and variant doesn't have a price in this currency

`Variant#price_in(currency)` will return nil if there’s no price for a
specified currency so `LineItem#update_price_from_modifier` will return
nil error

ayb/spree,imella/spree,ayb/spree,imella/spree,ayb/spree,imella/spree,ayb/spree