Fix client hash calculation during initial build for Cordova

Including an empty PUBLIC_SETTINGS object when there are no public
settings fixes a discrepancy between the way we calculated the client
hash for Cordova in CordovaBuilder and in webapp_server.js. This
discrepancy meant a Cordova app would always download a new version the
first time it started up, because the bundled version hash and the
server version hash would be different.

tools/cordova/builder.js

@@ -383,9 +383,7 @@ export class CordovaBuilder {
       release.current.isCheckout() ? "none" : release.current.name;
 
     let configDummy = {};
-    if (publicSettings) {
-      configDummy.PUBLIC_SETTINGS = publicSettings;
-    }
+    configDummy.PUBLIC_SETTINGS = publicSettings || {};
 
     const { WebAppHashing } =
       isopackets.load('cordova-support')['webapp-hashing'];