[SubtitleSampleReader] Restored old pts workaound

[CastagnaIT]

Description

This problem has been hidden since early ISA versions,
but it was highlighted when i reworked Dash parser and introduced also EXT-X-PROGRAM-DATE-TIME on HLS
the main problem is on DTSorPTS() comparison

inputstream.adaptive/src/Session.cpp

Lines 1067 to 1069 in a82e3eb

	{
	if (!res || streamReader->DTSorPTS() < res->GetReader()->DTSorPTS())
	{

we are comparing audio/video/subtitles,
for audio/video the pts/dts come from demuxer, but subtitles use pts from manifest or from subtitle data "cue" timing
these values not always are comparable with audio/video, because pts/dts that come from demuxer packet data
can be different and makes this package selection totally ineffective

other details on comments:
#1507 (comment)
#1507 (comment)

this PR for now i restore the old behaviour by removing the period start pts from segment pts
this will result that the subtitle "packet" pts will have most of time always a lower pts compared to audio/video
and then will be processed immediately without any control

an appropriate solution will be needed in future
since i think that weird thing can happens anyway
for example with all uses of lastPts variable:

inputstream.adaptive/src/main.cpp

Line 396 in a82e3eb

m_lastPts = sr->PTS();

that need to be at same time re-checked

Motivation and context

"fix" #1419 (comment)
"fix" #1507 (comment)

How has this been tested?

D+

Screenshots (if appropriate):

Types of change

• Bug fix (non-breaking change which fixes an issue)
• Clean up (non-breaking change which removes non-working, unmaintained functionality)
• Improvement (non-breaking change which improves existing functionality)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that will cause existing functionality to change)
• Cosmetic change (non-breaking change that doesn't touch code)
• None of the above (please explain below)

Checklist:

• I have read the Contributing document
• My code follows the Code Guidelines of this project
• My change requires a change to the Wiki documentation
• I have updated the documentation accordingly

[MauriceW67]

Downloaded the version with the fix from here:

https://jenkins.kodi.tv/blue/organizations/jenkins/xbmc%2Finputstream.adaptive/detail/PR-1522/1/artifacts

Can confirm Disney+ is showing subtitles again with this version. Thanks @CastagnaIT 👍

[glennguy]

Changes are fine. We have to think carefully regarding how to solve the problem outlined in todo comments