refactor: ParallelStructure.CalcQ: early return on error

refs #302

src/structure/parallel_structure.ts

@@ -116,6 +116,9 @@ export class ParallelStructure extends Nub {
         for (let i = 0; i < this._children.length; i++) {
             if (i !== iExcept) {
                 const res: Result = this._children[i].Calc("Q");
+                if (!res.ok) {
+                    return res;
+                }
                 qTot += res.vCalc;
                 // merge logs
                 calcRes.resultElement.log.addLog(res.log);