Merge pull request #84 from lucnygr/master

set HttpAsyncClientSingleton.HTTPC_CLIENT = null on shutdown

Author: a-schild

src/main/java/org/aarboard/nextcloud/api/utils/ConnectorCommon.java

@@ -273,6 +273,7 @@ public interface ResponseParser<R> {
     public static void shutdown() throws IOException {
             if(HttpAsyncClientSingleton.HTTPC_CLIENT != null) {
                 HttpAsyncClientSingleton.getInstance(null).close();
+                HttpAsyncClientSingleton.HTTPC_CLIENT = null;
             }		
     }
 }