2.6.21 Black frames at start even if cutting at I-frame

[Ryoandr]

If I cut at I-frame, sometimes I get black frames, until the next I-frame (in copy mode). It only affects the first cut for some reason.

[eumagga0x2a]

If the latest nightly exhibits the same issue, please provide a sample source video and exact stept to reproduce.

[Ryoandr]

Alright, tested avidemux_r170727_win64Qt5_452 and the cut is ok ! Tested on several other files that gave me black frames and all worked.