Subtitles: Make both DVD subtitles show in case of overlap

Makes behavior consistent with VLC and mplayer/libavcodec DVD
subtitle implementations. Sets the StopTime of the subtitle
before the same as the StartTime of the currently added DVD
subtitle.

Backport of MPC-HC commit f478e57

src/subtitles/VobSubFile.cpp

@@ -2241,6 +2241,16 @@ void CVobSubStream::Add(REFERENCE_TIME tStart, REFERENCE_TIME tStop, BYTE* pData
 		m_subpics.RemoveTail();
 		m_img.iIdx = -1;
 	}
+
+	// We can only render one subpicture at a time, thus if there is overlap
+	// we have to fix it. tStop = tStart seems to work.
+	if (m_subpics.GetCount() && m_subpics.GetTail()->tStop > p->tStart) {
+		TRACE(_T("[CVobSubStream::Add] Vobsub timestamp overlap detected! ")
+			  _T("Subpicture #%d, StopTime %I64d > %I64d (Next StartTime), making them equal!\n"),
+			  m_subpics.GetCount(), m_subpics.GetTail()->tStop, p->tStart);
+		m_subpics.GetTail()->tStop = p->tStart;
+	}
+
 	m_subpics.AddTail(p);
 }