OpenAI: set model parameters max/min

Problem

Setting model parameters with min or max parameter value is not possible for float or int parameters because of wrong value check for 0 in the validation function.

In addition to the above problem, the useDefaultMsg and useSystemMsgs are not respected on saving the form.

Solution

0 is valid value for float parameters. Instead of setting it to default use 0 as param value in case it is set from the UI.