Transition state incorrectly has continuous line with missing_is_hidden: true

[brianwebb11]

I am using MG 2.10. I have the following configuration:

        transition_on_update: true,
        missing_is_hidden: true,

I have segments of the data that are missing in the time series data. During the transition, the line appears to temporarily switch to missing_is_hidden = false state. Before and after the transition correctly do not show line segments for missing data. However, the transition state incorrectly has a continuous line.

[almossawi]

This commit fixes it, though I wonder whether the custom tween function is necessary anymore.

[brianwebb11]

Thanks!