Don't process frames in directories with long names

[gitgash]

How to reproduce:

1. create directory " 0001884_000000_20211110-112512_1025h_1_0_3.966666666666667_angle"
2. Place some frames to it
3. denseflow 0001884_000000_20211110-112512_1025h_1_0_3.966666666666667_angle-11 -b20 -a=tvl1 -s=1 -if -v

Result:
"0001884_000000_20211110-112512_1025h_1_0_3.966666666666667_angle-11", frames ≈ 31
push frames gray, video_flow_idx 0, batch_size 31
loaded video "0001884_000000_20211110-112512_1025h_1_0_3.966666666666667_angle-11", 31 frames
load frames exit.
1 videos (31 frames, 30 tvl1 flows) processed, using 48.381s, decoding speed 0.640747fps, flow speed 0.620078fps

But no flowXXX files created.