Clear scrollable timer when component unmounts (#219)

Fixes "null is not an object (evaluating 'n.rlv.scrollToIndex') in Scroller.js:155"

src/Scroller.js

@@ -32,6 +32,8 @@ export default class CalendarScroller extends Component {
   constructor(props) {
     super(props);
 
+    this.timeoutResetPositionId = null;
+
     this.updateLayout = renderDayParams => {
       const itemHeight = renderDayParams.size;
       const itemWidth = itemHeight + renderDayParams.marginHorizontal * 2;
@@ -67,6 +69,13 @@ export default class CalendarScroller extends Component {
     };
   }
 
+  componentWillUnmount() {
+    if (this.timeoutResetPositionId !== null) {
+      clearTimeout(this.timeoutResetPositionId);
+      this.timeoutResetPositionId = null;
+    }
+  }
+
   componentDidUpdate(prevProps, prevState) {
     let newState = {};
     let updateState = false;
@@ -151,7 +160,8 @@ export default class CalendarScroller extends Component {
         this.rlv.scrollToIndex(i, false);
         // RecyclerListView sometimes returns position to old index after
         // moving to the new one. Set position again after delay.
-        setTimeout(() => {
+        this.timeoutResetPositionId = setTimeout(() => {
+          this.timeoutResetPositionId = null;
           this.rlv.scrollToIndex(i, false);
           this.shifting = false; // debounce
         }, 800);