HLSReader: Only try to combine overlapping playlists if the diff is >= 0

Otherwise `Inew += diff` results in going off the front of the array and a crash.

Refs #13488
Signed-off-by: Paul Harrison <pharrison@mythtv.org>
(cherry picked from commit a59a4f0)

mythtv/libs/libmythtv/recorders/HLS/HLSReader.cpp

@@ -564,7 +564,7 @@ bool HLSReader::ParseM3U8(const QByteArray& buffer, HLSRecStream* stream)
                     --Iseg;
 
                 int64_t diff = (*Iseg).Sequence() - (*Inew).Sequence();
-                if (new_segments.size() > diff)
+                if (diff >= 0 && new_segments.size() > diff)
                 {
                     Inew += diff;