getRadioCheckedState - use is_null instead of !

[szwagros]

When checking if request has specified variable:

if ($this->missingOldAndModel($name) && !$request)

using negation operator gives wrong results if request has variable but it's value is for example 0 - which I believe is very common with radio input.

Changing it to:

if ($this->missingOldAndModel($name) && is_null($request))

solves this issue.

[rogermui]

Looks like it was missed when checkbox was fixed in #453.

[mvaraujo]

Looks like it was missed when checkbox was fixed in #453.

I fixed #453 three years ago, for check-boxes, and did not have the time to test the radio-buttons. Well, here we are :-)

I just submitted a pull request.

Thanks for the ticket and have good coding.