avcodec audio decoder: stricter PTS output

Only trust demuxer PTS if it is higher than what we expected
Fix demuxers that send several packets with identical PTS
Close #8453

Manual Cherry-Pick from a3898d68fd7a06d516a3feb3f11e2403dc741b81
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/codec/avcodec/audio.c

@@ -351,7 +351,7 @@ aout_buffer_t * DecodeAudio ( decoder_t *p_dec, block_t **pp_block )
         date_Init( &p_sys->end_date, p_sys->p_context->sample_rate, 1 );
 
     if( p_block->i_pts != 0 &&
-        p_block->i_pts != date_Get( &p_sys->end_date ) )
+        p_block->i_pts > date_Get( &p_sys->end_date ) )
     {
         date_Set( &p_sys->end_date, p_block->i_pts );
     }