IndexOutOfBoundsException in TraceData

[qiyitang71]

Original report by Qiyi Tang (GitHub: qiyitang71).

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In the TraceData

private void processChoiceGenerator(ChoiceGenerator<?> cg, int prevThreadIdx, int pi, int height, ThreadInfo ti) {
    // thread start/join highlight
    if (cg.getId() == "START" || cg.getId() == "JOIN") {
        if (lineTable.get(pi).getTextLine(height - 1).isSrc()) {
            threadStartSet.add(new Pair<>(pi, height - 1));
        }
    }

height can be zero which gives rise to an IndexOutOfBoundsException.