Fix #110333: Sound strip length not correct when opening old file

Commit `c9be925f7d` fixed files for studio, that were saved in incorrect
state. This also attempted to fix unaffected files.
In affected files `seq->startofs` did overflow. Sound strips are not
expected to have negative `startofs` and therefore fix in `c9be925f7d`
can be limited to broken files by checking `startofs` value.

source/blender/blenloader/intern/versioning_300.cc

@@ -1764,7 +1764,12 @@ static bool version_seq_fix_broken_sound_strips(Sequence *seq, void * /*user_dat
 
   seq->speed_factor = 1.0f;
   SEQ_retiming_data_clear(seq);
-  seq->startofs = 0.0f;
+
+  /* Broken files do have negative start offset, which should not be present in sound strips. */
+  if (seq->startofs < 0) {
+    seq->startofs = 0.0f;
+  }
+
   return true;
 }