CB-11880 android: Fail-safe for cordova.exec()

- added preliminary sanity check on args variable
- replication of iosExec() behaviour
- allows to call cordova.exec() without args variable

This closes #334

cordova-js-src/exec.js

@@ -78,6 +78,9 @@ function androidExec(success, fail, service, action, args) {
         androidExec.setJsToNativeBridgeMode(jsToNativeModes.JS_OBJECT);
     }
 
+    // If args is not provided, default to an empty array
+    args = args || [];
+
     // Process any ArrayBuffers in the args into a string.
     for (var i = 0; i < args.length; i++) {
         if (utils.typeName(args[i]) == 'ArrayBuffer') {