Check if there is a valid _activeVehical to not get a nullpointer exception

[Kaffelat]

Check to see if activeVehicle is null as that could cause a null exception when we don't.

Description

If a null vehicle was given to a joystick on creation the start-pulling function would eventually cause a null exception when it got to the _handleAxis function because we check if _activeVehical has joystickEnabled but not if the _activeVehical null.

Test Steps

1. Make a slot that waits for the joystickManager to send out that a new joystick have been connected
2. Make a Vehical that is null
3. Start polling on the newly connected joystick with the null Vehical
   Before that, the program would crash because of a null pointer exception. Now it keeps running and allows users to test the joysticks's raw value output if they desire

Checklist:

• Review Contribution Guidelines.
• Review Code of Conduct.
• I have tested my changes.

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