Wrong velocity recording when moving from invalid to valid datapoint

[grig-guz]

In https://github.com/ATUAV/EMDAT/blob/531463adde8aeb730b9ab5130f94d344880dcdd1/src/EMDAT_eyetracker/TobiiV3Recording.py#L19
when calculating pupil velocity, there is no check whether last_pupil is -1 or not. Consequently, for 1 velocity recording, we can get abnormal velocity.