FGManager: Update VSFilter/XySubFilter blocking routines

No longer disable VSFilter with madVR + XySubFilter, and add XySubFilter's
autoloader to be blocked when ISR is enabled as newer versions depend on
that.
Always prefer internal subtitle renderer

ISR does work fine not only with EVR so it can be safely used on XP also.
Move try/catch where it belong to be.
Fix ISR loading

- Fix ISR being auto-loaded when it shouldn't be.
- Fix ISR loading when auto-loading is disabled.
Disable some UI elements when ISR is unavailable or auto-loading is disabled.
Apply astyle
Prevent ISR from loading if VSFilter is already present.