Make InstancesEditor initialization more robust against new react-dnd versions

newIDE/app/src/InstancesEditor/ScrollbarContainer.js

@@ -34,7 +34,7 @@ const styles = {
 
 type ScrollableComponent = {
   scrollTo: (number, number) => void,
-  getViewPosition: () => ViewPosition,
+  getViewPosition: () => ?ViewPosition,
 };
 
 type Props = {
@@ -121,7 +121,9 @@ export const addScrollbars = (WrappedComponent: any) => {
     };
 
     _handleViewPositionChange = throttle(
-      (viewPosition: ViewPosition) => {
+      (viewPosition: ?ViewPosition) => {
+        if (!viewPosition) return;
+
         this._setAndAdjust({
           xValue: viewPosition.getViewX(),
           yValue: viewPosition.getViewY(),

newIDE/app/src/InstancesEditor/index.js

@@ -37,6 +37,22 @@ export default class InstancesEditorContainer extends Component {
   }
 
   componentDidMount() {
+    // Initialize the PIXI renderer, if possible
+    if (this.canvasArea && !this.pixiRenderer) {
+      this._initializeCanvasAndRenderer();
+    }
+  }
+
+  componentDidUpdate() {
+    // Initialize the PIXI renderer, if not already done.
+    // This can happen if canvasArea was not rendered
+    // just after the mount (depends on react-dnd versions?).
+    if (this.canvasArea && !this.pixiRenderer) {
+      this._initializeCanvasAndRenderer();
+    }
+  }
+
+  _initializeCanvasAndRenderer() {
     this.pixiRenderer = PIXI.autoDetectRenderer(
       this.props.width,
       this.props.height
@@ -544,7 +560,7 @@ export default class InstancesEditorContainer extends Component {
     );
   };
 
-  getViewPosition = () => {
+  getViewPosition = () /*: ?ViewPosition */ => {
     return this.viewPosition;
   };