Fix say-all with oneCore synth (PR #13652)
Fixes #13651
Summary of the issue:
Starting say-all with synth set to onecore failed with an error.
A logic error in the PR #13634
Caused the "markerStr" to be constructed incorrectly.
The | character expected to separate entries was missing.
Example string: 20:1437521:18864375
Should be instead: 20:14375|21:18864375
Description of change:
Fix the logic error, every entry after the first should start with a | character.
