Executable file created by Pyxel Packager does not work
**Describe the bug**
There is a flicker of pyxel window after runnung the excutable file created by Pyxel Packager.

**To Reproduce**
Steps to reproduce the behavior:
1. Use 'pyxelpackager main.py' in terminal.
2. 'main.exe' created under 'dist' folder.
3. Copy related '.pyxres' file into path '/dist/assets'
3. Double click 'main. exe'
4. Error: A flicker of pyxel window. 


**Expected behavior**
The file can be correctly executed thru the origin 'main.py'. The newly created 'main.exe' is expected to work.

**Screenshots**
![微信图片_20191122031725](https://user-images.githubusercontent.com/57948041/69369274-bc4e3c80-0cd6-11ea-88e7-a30f807c10cf.png)
(screenshot when executed 'pyxelpackager main.py')


**Desktop (please complete the following information):**
 - OS: Windows 10
- Browser: 360极速浏览器
 - Version:  11


**Additional context**
To make sure of putting the resource file in the correct path, I tried to put it in path '/dist' and also in path '/dist/assets'. However, in both cases, the same error occurs.
