AttributeError on sitePublish on Linux

```
- Libsecpk256k1 loaded: CompiledLib in 0.028s
- Version: 0.7.1 r4206, Python 3.7.3 (default, Mar 27 2019, 22:11:17)
[GCC 7.3.0], Gevent: 1.4.0
SiteManager Deleting orphan site from content.db: 1Name2NXVi1RDPDgf5617UoW7xA6YrhM9F
SiteManager Deleting orphan site from content.db: 1DvxA4WP2jbBaZbTebV1RufMLhTTqDhVUQ
- Loading site...
- Unhandled exception: 'NoneType' object has no attribute 'settings'
Traceback (most recent call last):
File "/builds/wizardforcel/zeronet-uploader/ZeroNet-linux-dist-linux64/core/zeronet.py", line 17, in main
main.start()
File "/builds/wizardforcel/zeronet-uploader/ZeroNet-linux-dist-linux64/core/src/main.py", line 537, in start
actions.call(config.action, action_kwargs)
File "/builds/wizardforcel/zeronet-uploader/ZeroNet-linux-dist-linux64/core/src/main.py", line 121, in call
back = func(**kwargs)
File "/builds/wizardforcel/zeronet-uploader/ZeroNet-linux-dist-linux64/core/src/main.py", line 381, in sitePublish
site.settings["serving"] = True # Serving the site even if its disabled
AttributeError: 'NoneType' object has no attribute 'settings'
```

从 core/src/main.py 的 sitePublish（约第 381 行）开始，跟踪在访问其设置之前 site 对象是如何获取的。在报告的环境中于 Linux 上复现 sitePublish 操作，并确定它为什么是 None；完成的标准是该操作在不出现此 AttributeError 的情况下完成。

由索引模型根据 Issue 内容生成。