Test upload of empty files
Test upload of empty files

- Cover upload of empty file of zero size with tests
- Cover form submission of blank file field with tests
- Resolve #2778 Cannot upload empty file or blank file field

LinkedDestiny/swoole-src,LinkedDestiny/swoole-src,swoole/swoole-src,LinkedDestiny/swoole-src,LinkedDestiny/swoole-src,swoole/swoole-src,LinkedDestiny/swoole-src,swoole/swoole-src,swoole/swoole-src,swoole/swoole-src,swoole/swoole-src,LinkedDestiny/swoole-src,LinkedDestiny/swoole-src,swoole/swoole-src