Add empty 1st entry to Lechapt-Calmon materials (normalization for GUI forms)

src/lc-material.ts

 /** materials for Lechapt-Calmon */
 export enum LCMaterial {
+    NONE,
     UnlinedCastIronCoarseConcrete,
     CastSteelOrUncoatedCoarseConcrete,
     CastSteelOrCementCoating,

src/pipe_flow/lechaptcalmon.ts

@@ -143,10 +143,12 @@ export class LechaptCalmon extends Nub implements Observer {
      */
     private applyMaterialPreset() {
         const m = this.properties.getPropValue("material");
-        const values = LechaptCalmon._materials[m];
-        this.prms.L.singleValue = values.L;
-        this.prms.M.singleValue = values.M;
-        this.prms.N.singleValue = values.N;
+        if (m > 0) {
+            const values = LechaptCalmon._materials[m - 1]; // "0" means no preset
+            this.prms.L.singleValue = values.L;
+            this.prms.M.singleValue = values.M;
+            this.prms.N.singleValue = values.N;
+        }
     }
 
 }