Fix filters with encapsulated transitions corrupting frame position.

Filters that use an encapsulated transition were modifying the frame position. Other filters that rely on the frame position would get an incorrect value.

Test case:
melt -producer frei0r.test_pat_B -filter wave -filter watermark:"+hi.txt" in=200 out=400
At frame 200 the wave would "jump" because the wave phase is calculated from frame position which gets modified by the watermark filter.