Resolve "Section paramétrée: crash de l'appli sur variation de paramètre"

Closes #561 (closed)

src/app/results/var-results.ts

@@ -355,7 +355,9 @@ export class VarResults extends CalculatedParamResults implements PlottableData
         // result keys (extra or not) - some lines might miss some results, in case of an error;
         // use those keys to ensure all columns are filled
         if (this.resultKeys.length === 0) {
-            this.resultKeys.push(this.result.symbol);
+            if (this.result.symbol !== undefined) {
+                this.resultKeys.push(this.result.symbol);
+            }
             for (const re of this.result.resultElements) { // re:ResultElement
                 for (const erk in re.values) {
                     if (!this.resultKeys.includes(erk)) {