Handle out of bound history entries + fix last known entry (#251)

* Make sure values out of bound are inserted into res[0] (caused by Math.abs)

* Only keep the latest out of bound entry

src/graph.js

@@ -48,6 +48,9 @@ export default class Graph {
 
     const coords = this._history.reduce((res, item) => this._reducer(res, item), []);
 
+    // drop potential out of bound entry's except one
+    if (coords[0] && coords[0].length) coords[0] = [coords[0][coords[0].length - 1]];
+
     // extend length to fill missing history
     const requiredNumOfPoints = Math.ceil(this.hours * this.points);
     coords.length = requiredNumOfPoints;
@@ -60,7 +63,7 @@ export default class Graph {
   _reducer(res, item) {
     const age = this._endTime - new Date(item.last_changed).getTime();
     const interval = (age / ONE_HOUR * this.points) - this.hours * this.points;
-    const key = Math.floor(Math.abs(interval));
+    const key = interval < 0 ? Math.floor(Math.abs(interval)) : 0;
     if (!res[key]) res[key] = [];
     res[key].push(item);
     return res;