fix decode HEVC format description

[juicechu]

If I change the script from rtc_use_h265=false to rtc_use_h265=true, I found the H265 decode is broken. I get the error message is "Missing video format. Frame with sps/pps required. ". So that is caused by the decoding the HEVC format not correctly.

[jianjunz]

Thanks for reporting this issue. If video format is not available at receiver side, it sends a key frame request to the sender. Did you observe this error even a key frame is received?

[panjekm]

I just had the same issue and found the same solution, I did the change in sdk/objc/components/video_codec/RTCVideoDecoderH265.mm to actually call the description function of H265, this made the video stream work. Would be great if this fix could be merged.