BF: Fix sequence stacking warning in LiFE tracking
BF: Fix sequence stacking warning in LiFE tracking

Fix sequence stacking warning in LiFE tracking

Fixes:
```
FutureWarning: arrays to stack must be passed as a "sequence" type such as list
or tuple. Support for non-sequence iterables such as generators is deprecated as
of NumPy 1.16 and will raise an error in the future.
```

raised for example in
https://dev.azure.com/dipy/46625eaf-7255-4a2c-9e92-befcdbdca2a8/_apis/build/builds/293/logs/262

FrancoisRheaultUS/dipy,FrancoisRheaultUS/dipy