Fix order preview reporting for more order types

This has been broken for years and it was finally tracked down thanks to
contributor in #42.

Problem was just the value we compared against is the raw IBKR API
protocol value, but the comparison was expecting a parsed standard max
float value we use everywhere else.

Solution is just to parse the inbound float so it becomes a native value
to compare against first.

The impact of the problem was `whatIf` orders only worked for limit
orders previously. Attempting to run a preview `whatIf` order on other
order types always just returned bad values and couldn't show previews
and wouldn't report potential commission or margin impacts. Now the
`whatIf` orders run and execute fully so the caller receives a
completely populated `OrderState` object with all fields properly
populated.

According to the API patterns, these fields are _always_ numeric from
the API (which is why IBKR just uses "max float" to mean "no data") so
we should _always_ be able to `float()` parse the field without any
problems. If the API ever returns non-float-data then this will
obviously do weird things, but so far the upstream IBKR API doesn't
appear to be able to inject non-float values into these fields.

Fixes #42

Author: mattsta

ib_async/wrapper.py

@@ -495,7 +495,7 @@ def openOrder(
         """
         if order.whatIf:
             # response to whatIfOrder
-            if orderState.initMarginChange != str(UNSET_DOUBLE):
+            if float(orderState.initMarginChange) != UNSET_DOUBLE:
                 self._endReq(order.orderId, orderState)
         else:
             key = self.orderKey(order.clientId, order.orderId, order.permId)