Check the type of the source before using it

This satisfies tsc in addition to making the class more defensive
against source types that it does not support.

src/ol/renderer/webgl/TileLayer.js

@@ -7,6 +7,7 @@
 import LayerType from '../../LayerType.js';
 import TileRange from '../../TileRange.js';
 import TileState from '../../TileState.js';
+import TileSource from '../../source/Tile.js';
 import {numberSafeCompareFunction} from '../../array.js';
 import {createEmpty, intersects} from '../../extent.js';
 import {roundUpToPowerOfTwo} from '../../math.js';
@@ -152,6 +153,10 @@ class WebGLTileLayerRenderer extends WebGLLayerRenderer {
 
     const tileLayer = /** @type {import("../../layer/Tile.js").default} */ (this.getLayer());
     const tileSource = tileLayer.getSource();
+    if (!(tileSource instanceof TileSource)) {
+      return true;
+    }
+
     const tileGrid = tileSource.getTileGridForProjection(projection);
     const z = tileGrid.getZForResolution(viewState.resolution);
     const tileResolution = tileGrid.getResolution(z);