fix bug of NPL in MoGoLiveManager

foudations/mogo-live/src/main/java/com/mogo/cloud/live/manager/MoGoLiveManager.java

@@ -367,10 +367,13 @@ public class MoGoLiveManager {
      * 退出房间
      */
     private void logOutRoom() {
+        if (mExpressEngine == null) {
+            return;
+        }
         if (!TextUtils.isEmpty(currentRoomId)) {
             mExpressEngine.logoutRoom(currentRoomId);
         }
-        if(customVideoCaptureConfig == null){
+        if (customVideoCaptureConfig == null) {
             // 创建自定义视频采集对象
             customVideoCaptureConfig = new ZegoCustomVideoCaptureConfig();
             // 设置自定义视频采集视频帧数据类型
@@ -459,7 +462,10 @@ public class MoGoLiveManager {
      * 停止预览
      */
     private void stopPreview() {
-        ZegoExpressEngine.getEngine().stopPreview();
+        if(mExpressEngine == null){
+            return;
+        }
+        mExpressEngine.stopPreview();
     }
 
     /**
@@ -474,8 +480,11 @@ public class MoGoLiveManager {
      * 停止推送数据
      */
     private void stopPublishingStream() {
+        if(mExpressEngine == null){
+            return;
+        }
         // 停止推送
-        ZegoExpressEngine.getEngine().stopPublishingStream();
+        mExpressEngine.stopPublishingStream();
     }
 
     /**