Minor potential bug in add_gg

[JohMast]

add_gg, Line 121: If working with a very short number of frames, if(length(gg) != length(frames)) gg <- rep(list(gg), length(frames)) can evaluate to FALSE, because the number of frames happens to be the same as the number of gg expressions. In that case no repeated list will be created.

This would probably never happen in practice, but perhaps a more precise check can be found.