Don't abort client init when GenesisConfig is already initialized

This way one can initialize the GenesisConfig for mainnet before starting the client, and then use the demo page to connect to the mainnet.

index.html

@@ -60,8 +60,13 @@
     nimiqInitPromise.then(async () => {
         document.getElementById('message').innerText = 'Nimiq loaded. Connecting and establishing consensus.';
 
-        // Connect to the testnet.
-        Nimiq.GenesisConfig.test();
+        try {
+            // Try to connect to the testnet.
+            Nimiq.GenesisConfig.test();
+        } catch (error) {
+            console.error(error);
+            // Don't fail if GenesisConfig has already been initialized (e.g. for mainnet).
+        }
 
         const $ = {};
         window.$ = $;