MoCap time offset is changed when read in

If you read an already saved MoCap-File, its time offset is changed. This is because the time offset from the MoCap-file (i.e. firstFrame and lastFrame from C3D) is saved in the same member as the time offset chosen by the user. This makes it hard to know, if you still need to apply the file offset (first time loading) or if it already was applied (second or later time loading).