Billing/GraphEntry: Use 73 Oe as MinX for gebunden graph

Elwig/Helpers/Billing/GraphEntry.cs

@@ -35,7 +35,7 @@ namespace Elwig.Helpers.Billing {
             this(id, curve.Mode, minX, maxX) {
             DataGraph = new Graph(curve.Normal, minX, maxX);
             if (curve.Gebunden != null)
-                GebundenGraph = new Graph(curve.Gebunden, minX, maxX);
+                GebundenGraph = new Graph(curve.Gebunden, 73, maxX);
             Contracts = contracts;
         }