Don't add zero-length bars when transitions are off

[nicolaskruchten]

We need to resolve plotly/orca#345 and it seems like we need to carve out a part of #4180 that adds 0-length bars for transitions. In the static-image-export case these bars are not required and cause rendering artifacts downstream.

We could either: check if layout.transition isn't set and if so not show those bars OR remove those bars in the saveImage code.