remove multiple frames from generated thumbnails (vizzu-lib 0.8)

[andraskangyal]

Black frames: drilldown_01.mp4, drilldown_to_main_05_pol.mp4, drilldown_to_main_05.mp4, drilldown_to_main_ORI_07.mp4, drilldown_to_main_sub_03.mp4, drilldown_to_main_sub_04.mp4, drilldown_to_sub_02_pol.mp4, drilldown_to_sub_02.mp4, drilldown_to_sub_11.mp4, drilldown_to_sub_12_pol.mp4, drilldown_to_sub_12.mp4, ...

[veghdev]

outdated