Fix to JsonUtil to properly handle java Lists

This fixes a bug in FirebaseDB where a list of lists is handed to the
AppendValue block.

Change-Id: I16cd4612f978842e62a719627bc729d8f4a48d90

appinventor/components/src/com/google/appinventor/components/runtime/FirebaseDB.java

@@ -764,7 +764,7 @@ public class FirebaseDB extends AndroidNonvisibleComponent implements Component
           if (value instanceof List) {
             ((List)value).add(valueToAdd);
             try {
-              value = JsonUtil.getJsonRepresentation(YailList.makeList((List)value));
+              value = JsonUtil.getJsonRepresentation((List)value);
             } catch (JSONException e) {
               result.err = "Could not convert value to JSON.";
               return Transaction.abort();

appinventor/components/src/com/google/appinventor/components/runtime/util/JsonUtil.java

@@ -177,6 +177,9 @@ public class JsonUtil {
     if (value instanceof Boolean) {
       return value.toString();
     }
+    if (value instanceof List) {
+      value = ((List)value).toArray();
+    }
     if (value.getClass().isArray()) {
       StringBuilder sb = new StringBuilder();
       sb.append("[");