Fix issue with timestamp translation.

The timestamp translation code has an error in it -- it only applies a correction to the fourth and last number of the timestamp, whereas the whole timestamp needs to be corrected. This bug results in timecode drift when using SCCReader if the source is non-drop-frame. Here is a fix for it. (This is still not 100% accurate since drop-frame timebase is not linearly mapped to wall clock time, but as a first approximation it works better.)