[Classic] Bug when trying to access values in registeredBarData for bars that don't exist in Classic

[brittyazel]

In Neuron-DB-Defaults.lua line 285, we declare a blizzBars table where we define ExtraBar, ExitBar, and ZoneAbilityBar. This table is then used in InterfacePanel.lua in the guiOptions() function (line 123) where it will throw errors on wow Classic due to those three bar types not being supported, as we specify earlier in Neuron-RegisteredBarData.lua.

We should fix this logic so that guiOptions() is not trying to access elements in our registered bars table that doesn't exist.