Cannot enable video via pjsua_call_reinvite2()/update2()

[nanang]

Reproducing steps:

1. A makes a video call to B, with vid_cnt == 1 in the call setting.
2. B rejects the video
3. A tries to enable video by sending re-INVITE with vid_cnt == 1 in the new call setting.
4. The SDP offer sent by A still has video media line disabled (port zero).

After investigation, the SDP generation for the re-INVITE doesn't initialize the video media, technically because the pjsua_media_channel_init() is skipped due to "no update" on media count setting (vid_cnt in this case). So it is the check of media-count-update that is actually buggy.

Thanks Itay Bianco for the report.