Reimport FBX does not correctly update frame-rate

This is an issue with the sequencer model, it does not clear its bPopulated flag so doesn't allow for changing the frame-rate to a non-compatible (multiple/factor off FPS).

1. Import an FBX (containing 30fps data) using custom sample rate of 24
2. Open the resulting animation sequence
3. Change the import settings to use automatic frame rate selection
4. Reimport the animation

Expected result: animation is stored and sampled at 30fps

Found result: animation is stored and sampled at 24fps