Fixes 32 Seg Faults with LiveTV on some platforms

[jksj461]

LiveTV-SegFault.txt
The file contains the gdb output for a segfault that occurs on any attempt to access live tv on a remote Intel Desktop.
Note LiveTV is working on Android 32 (Nvidia Shield & Fire Stick Max) also on a slow Intel Notebook.
It could be noteworthy that the log shows two files being accessed :-
'myth://tv/20681_20220208170148.ts
myth://tv/20681_20220208170150.ts
normally the target file only contains 2 secs of data but with the frontend running under the debugger the backend continues to write valid data .
The file 20681_20220208171500.ts does contain a valid recording

[bennettpeter]

I tried to recreate this but I am unable to. Did you start Live TV from the LiveTV menu or from the program guide? I tried both and it works for me. If you tried from the menu please try also from the program guide and see if that makes a difference.

[jksj461]

High it segfaults instantly with live tv accessed by either method. The same build mythtv-light_32~Pre-3519-g0caf3ac0ec-0_amd64_focal.deb runs happily on an Intel Notebook. Which does suggest that there is a bad runtime link of some kind on this machine, if the multi file creates mentioned above is a red herring.
I installed the full debug version from the Ubuntu ppa to compare. No change in behaviour but the trace may offer more clues.
The line

0x00007ffff793c0ba in StreamHasRequiredParameters (Stream=0x555556379680, Context=0x555556468540) at decoders/avformatdecoder.cpp:238
238 decoders/avformatdecoder.cpp: No such file or directory.
May be significant

LiveTV-SegFaultPPA.txt

[paul-h]

@bennettpeter This appears to be a result of the change to support ffmpeg 4.4.2 from 3 months ago

It looks like internal may be NULL or invalid here? https://github.com/MythTV/mythtv/blame/master/mythtv/libs/libmythtv/decoders/avformatdecoder.cpp#L238

[bennettpeter]

There was a change from Stream->nb_decoded_frames to Stream->internal->nb_decoded_frames due to ffmpeg moving some fields to internal. If internal null is indeed causing the bug then we should comment that check as has been done to the ones above it.