Pass ETH signer only if it can actually sign

We have seen an "no accounts" invalid operation getAddress when trying
to call a contract function in the init calls.
It seems ethers has a problem with a signer that does not have any
accounts - even though we don't try to sign an actual transaction and
only read data from the contract.

This change only passes the signer if we have an unlocked web3 provider
(metamask).

app/services/kredits.js

@@ -38,36 +38,38 @@ export default Service.extend({
         );
         ethProvider.listAccounts().then((accounts) => {
           this.set('currentUserAccounts', accounts);
-          resolve(ethProvider);
+          const ethSigner = accounts.length === 0 ? null : ethProvider.getSigner();
+          resolve({
+            ethProvider,
+            ethSigner
+          });
         });
       } else {
         console.debug('[kredits] Creating new instance from npm module class');
         networkId = parseInt(config.contractMetadata.networkId);
+        console.debug(`[kredits] networkId=${networkId} providerURL: ${config.web3ProviderUrl}`);
         ethProvider = new ethers.providers.JsonRpcProvider(
           config.web3ProviderUrl,
           { chainId: networkId }
         );
-        resolve(ethProvider);
+        resolve({
+          ethProvider: ethProvider,
+          ethSigner: null
+        });
       }
     });
   },
 
   setup() {
-    return this.getEthProvider().then((ethProvider) => {
+    return this.getEthProvider().then((providerAndSigner) => {
-      let ethSigner;
 
-      if (ethProvider.getSigner) {
+      let kredits = new Kredits(providerAndSigner.ethProvider, providerAndSigner.ethSigner, {
-        ethSigner = ethProvider.getSigner();
-      }
-
-      let kredits = new Kredits(ethProvider, ethSigner, {
         ipfsConfig: config.ipfs
       });
       return kredits
         .init()
         .then((kredits) => {
           this.set('kredits', kredits);
-
           if (this.currentUserAccounts && this.currentUserAccounts.length > 0) {
             this.getCurrentUser.then((contributorData) => {
               this.set('currentUser', contributorData);