in previouse if a log subsetcion not set level
it will use ``info`` as default value.
this pr will make default value (``[log] -> LEVEL``) useable.
example config:
```INI
[log]
MODE = console
LEVEL = Trace
[log.console]
LEVEL =
STDERR = false
```
previous result:
```JSON
// console:
{
"level": "info",
...................
}
```
after change:
```JSON
// console:
{
"level": "track",
...................
}
```
Signed-off-by: a1012112796 <1012112796@qq.com>
Co-authored-by: zeripath <art27@cantab.net>
Co-authored-by: Lauris BH <lauris@nix.lv>
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