Bug in ViCLIP's implementation + demo

[mannatsingh]

In https://github.com/OpenGVLab/InternVideo/blob/6264cc85f72e38dce7e38549182d0369c50cde00/Data/InternVid/viclip/viclip.py#L140-L143 a single video is converted to a batch of 8 images (instead of a batch of one video). This bug is transferred to the demo in https://github.com/OpenGVLab/InternVideo/blob/6264cc85f72e38dce7e38549182d0369c50cde00/Data/InternVid/viclip/init.py#L71 where the outputs for the incorrect batch size of 8 are thrown out and only the first frame's outputs are used.