Codechange: address CodeQL issue "Multiplication result converted to larger type" (#10306)

Most are very unlikely to ever be triggered in our codebase; two
stand out: linkgraph and money cheat. Those, potentially, could
wrap earlier than expected.

src/cheat_gui.cpp

@@ -56,7 +56,7 @@ static int32 _money_cheat_amount = 10000000;
  */
 static int32 ClickMoneyCheat(int32 p1, int32 p2)
 {
-	Command<CMD_MONEY_CHEAT>::Post(p2 * _money_cheat_amount);
+	Command<CMD_MONEY_CHEAT>::Post(Money(_money_cheat_amount) * p2);
 	return _money_cheat_amount;
 }