Fix #9440: negative cargo payments not being handled right

Cargo payments were stored as unsigned integer, but cast to int64 during
application of inflation. However, then being multiplied with a uint64
making the result uint64. So in the end the payment that should have been
negative becomes hugely positive.

src/economy.cpp

@@ -803,7 +803,7 @@ void RecomputePrices()
 
 	/* Setup cargo payment */
 	for (CargoSpec *cs : CargoSpec::Iterate()) {
-		cs->current_payment = ((int64)cs->initial_payment * _economy.inflation_payment) >> 16;
+		cs->current_payment = (cs->initial_payment * (int64)_economy.inflation_payment) >> 16;
 	}
 
 	SetWindowClassesDirty(WC_BUILD_VEHICLE);