Fixing bug when no WebGL is available

The switch to Phaser 3.50 introduced a bug when WebGL is not available in a browser.
The changes in this commit prevent calls to the WebGL pipeline if the pipeline is not available.

front/src/index.ts

@@ -73,9 +73,10 @@ const config: GameConfig = {
     },
     callbacks: {
         postBoot: game => {
-            // FIXME: we should fore WebGL in the config.
-            const renderer = game.renderer as WebGLRenderer;
-            renderer.pipelines.add(OutlinePipeline.KEY, new OutlinePipeline(game));
+            const renderer = game.renderer;
+            if (renderer instanceof WebGLRenderer) {
+                renderer.pipelines.add(OutlinePipeline.KEY, new OutlinePipeline(game));
+            }
         }
     }
 };