`scene.animation.time` is initialized to zero, which may have unexepected effect with time range not starting at zero

[mwestphal]

Describe the bug scene.animation.time is initialized to zero, which may have unexepected effect with time range not starting at zero

To Reproduce Steps to reproduce the behavior:

1. Open the file using f3d --dry-run negative_range_animated.e
2. File is already half animated

Expected behavior We should start at the beginning of the timerange of the animation

Additional context It is a secondary effect of #434 , we cant initialize the time to NaN because cxxopts does not support it