avformat/mov: Merge tts after building index for old-style uncompressed PCM

This was a regression introduced in 292c1df7c1.

Since we don't know the length of the stts data until after building the
index, since we're generating it, we need to merge any ctts data after,
since otherwise tts_count is set to 0, and no packets will be output.

We can't remove the merge entirely, because uncompressed PCM with
a ctts atom is technically valid (e.g. a constant CTS offset).

This fixes old-style uncompressed PCM demuxing.

Fixes #11490.

Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>

libavformat/mov.c

@@ -4841,10 +4841,6 @@ static void mov_build_index(MOVContext *mov, AVStream *st)
         if (!sc->chunk_count || sc->tts_count)
             return;
 
-        ret = mov_merge_tts_data(mov, st, MOV_MERGE_CTTS);
-        if (ret < 0)
-            return;
-
         // compute total chunk count
         for (i = 0; i < sc->stsc_count; i++) {
             unsigned count, chunk_count;
@@ -4939,6 +4935,10 @@ static void mov_build_index(MOVContext *mov, AVStream *st)
                 chunk_samples -= samples;
             }
         }
+
+        ret = mov_merge_tts_data(mov, st, MOV_MERGE_CTTS);
+        if (ret < 0)
+            return;
     }
 
     if (!mov->ignore_editlist && mov->advanced_editlist) {