#244 修复下载多媒体文件报错的问题

weixin-java-common/src/main/java/me/chanjar/weixin/common/util/http/MediaDownloadRequestExecutor.java

@@ -17,6 +17,7 @@ public abstract class MediaDownloadRequestExecutor<H, P> implements RequestExecu
   protected RequestHttp<H, P> requestHttp;
   protected File tmpDirFile;
   public MediaDownloadRequestExecutor(RequestHttp requestHttp, File tmpDirFile) {
+    this.requestHttp = requestHttp;
     this.tmpDirFile = tmpDirFile;
   }