properly handle responses other than 200, fixes #26

Fix for getting ClassCastException while downloading subtitles for an user whose daily limit is reached. In this case, the response contains boolean in data field:

Response: {seconds=0.004, data=false, status=407 Download limit reached}

NOTE: Fix for this bug introduces API incompatibility, ListResponse will now return Optional<List<T>> instead of List<T>.

diff --git a/src/main/java/com/github/wtekiela/opensub4j/response/ListResponse.java b/src/main/java/com/github/wtekiela/opensub4j/response/ListResponse.java
index 7718982..4433e7f 100644
--- a/src/main/java/com/github/wtekiela/opensub4j/response/ListResponse.java
+++ b/src/main/java/com/github/wtekiela/opensub4j/response/ListResponse.java
@@ -14,13 +14,14 @@ package com.github.wtekiela.opensub4j.response;

 import java.util.List;
 import java.util.Objects;
+import java.util.Optional;

 public class ListResponse<T> extends Response {

     @OpenSubtitlesApiSpec(fieldName = "data")
-    private List<T> data;
+    private Optional<List<T>> data;

-    public List<T> getData() {
+    public Optional<List<T>> getData() {
         return data;
     }

wtekiela / opensub4j

properly handle responses other than 200, fixes #26 #28