fix缩略图更新

controllers/sandbox/sandbox.go

@@ -1790,7 +1790,13 @@ func (this *SandboxController) SaveV2() {
 			ModifyTime:        time.Now(),
 			SandboxClassifyId: req.SandboxClassifyId,
 		}
-		var updateSandboxColumn = []string{"Content", "MindmapData", "PicUrl", "ModifyTime", "SandboxClassifyId"}
+		//缩略图为空时不更新
+		var updateSandboxColumn = []string{}
+		if req.PicUrl == ""{
+			updateSandboxColumn = []string{"Content", "MindmapData", "ModifyTime", "SandboxClassifyId"}
+		} else {
+			updateSandboxColumn = []string{"Content", "MindmapData", "PicUrl", "ModifyTime", "SandboxClassifyId"}
+		}
 		err = sandboxInfo.Update(updateSandboxColumn)
 		if err != nil {
 			br.Msg = "保存失败！"