Lazily create interim tiles (fixes most tests)

src/ol/VectorImageTile.js

@@ -103,8 +103,6 @@ class VectorImageTile extends Tile {
      */
     this.sourceTileListenerKeys_ = [];
 
-    this.sourceTilesLoaded = false;
-
     /**
      * Use only source tiles that are loaded already
      * @type {boolean}
@@ -150,7 +148,8 @@ class VectorImageTile extends Tile {
         this.finishLoading_();
       }
 
-      if (!this.sourceTilesLoaded && !useLoadedOnly) {
+      this.createInterimTile_ = function() {
+        if (this.getState() !== TileState.LOADED && !useLoadedOnly) {
           let bestZoom = -1;
           for (const key in sourceTiles) {
             const sourceTile = sourceTiles[key];
@@ -171,14 +170,22 @@ class VectorImageTile extends Tile {
           }
         }  
       }
+    }
 
   }
 
+  getInterimTile() {
+    if (!this.interimTile) {
+      this.createInterimTile_();
+    }
+    return super.getInterimTile();
+  }
+
   /**
    * @inheritDoc
    */
   disposeInternal() {
-    this.getInterimTile = super.getInterimTile;
+    delete this.createInterimTile_;
     this.state = TileState.ABORT;
     this.changed();
     if (this.interimTile) {

test/spec/ol/renderer/canvas/vectortilelayer.test.js

@@ -75,6 +75,7 @@ describe('ol.renderer.canvas.VectorTileLayer', function() {
         tileGrid: createXYZ()
       });
       source.getTile = function() {
+        arguments[1] = TileState.LOADED;
         const tile = VectorTileSource.prototype.getTile.apply(source, arguments);
         tile.setState(TileState.LOADED);
         return tile;
@@ -106,7 +107,7 @@ describe('ol.renderer.canvas.VectorTileLayer', function() {
       map.removeLayer(layer);
       map.addLayer(testLayer);
       const spy = sinon.spy(CanvasVectorTileLayerRenderer.prototype,
-        'getTransform');
+        'getRenderTransform');
       map.renderSync();
       expect(spy.callCount).to.be(0);
       spy.restore();
@@ -114,7 +115,7 @@ describe('ol.renderer.canvas.VectorTileLayer', function() {
 
     it('renders both replays and images for hybrid rendering', function() {
       const spy1 = sinon.spy(CanvasVectorTileLayerRenderer.prototype,
-        'getTransform');
+        'getRenderTransform');
       const spy2 = sinon.spy(CanvasVectorTileLayerRenderer.prototype,
         'renderTileImage_');
       map.renderSync();
@@ -129,7 +130,7 @@ describe('ol.renderer.canvas.VectorTileLayer', function() {
         renderer: function() {}
       }));
       const spy = sinon.spy(CanvasVectorTileLayerRenderer.prototype,
-        'getTransform');
+        'getRenderTransform');
       map.renderSync();
       expect(spy.callCount).to.be(1);
       spy.restore();