EmergenceCalculator crashes when player leaves the area; need more failsafes

[mearlboro]

Issue happening on feat/config-file branch (see #5), to be merged into main
Currently unable to reproduce with stored video, because the recording stopped once the calculator crashed.

The settings are stored in ICGH_testing.yml and the culprit footage is in 7.avi. The last frame of the video is where the error happened but the next frame has not been recorded due to the crash.

To run locally:

$ cd python
$ CONFIG_PATH='./camera/config/ICGH_testing.yml' python camera/server/server.py local

Exception in thread Thread-4:
Traceback (most recent call last):
  File "infodynamics.measures.continuous.gaussian.MutualInfoCalculatorMultiVariateGaussian.java", line -1, in infodynamics.measures.continuous.gaussian.MutualInfoCalculatorMultiVariateGaussian.computeLocalUsingPreviousObservations
  File "infodynamics.measures.continuous.gaussian.MutualInfoCalculatorMultiVariateGaussian.java", line -1, in infodynamics.measures.continuous.gaussian.MutualInfoCalculatorMultiVariateGaussian.computeLocalUsingPreviousObservations
Exception: Java Exception

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/usr/lib/python3.7/threading.py", line 917, in _bootstrap_inner
    self.run()
  File "/usr/lib/python3.7/threading.py", line 865, in run
    self._target(*self._args, **self._kwargs)
  File "/home/pi/camera/server/video.py", line 343, in tracking
    # compute emergence of positions and update psi
  File "/home/pi/camera/core/emergence.py", line 172, in update_and_compute
    psi = self.compute_psi(V)
  File "/home/pi/camera/core/emergence.py", line 150, in compute_psi
    psi -= calc.computeLocalUsingPreviousObservations(javify(Xip), jV)[0]
java.lang.java.lang.NullPointerException: java.lang.NullPointerException