When reading cookies from the browser, the user is able to give either just the browser name, or also provide profile/container information.
If an exact profile is provided, there is no need to find the latest profile with `os.walk` which is very expensive.
This change optimizes that case and the performance increase is significant (~8 sec to 0.6 sec).
```
$ time gallery-dl --config-ignore -d . -D . --cookies-from-browser FIREFOX https://imgur.com/OO4UNqJ
[cookies][info] Extracted 16 cookies from Firefox
./imgur_OO4UNqJ.jpg
real 0m8.429s
user 0m0.216s
sys 0m0.431s
$ time gallery-dl --config-ignore -d . -D . --cookies-from-browser FIREFOX:bgamf5r6.default-release https://imgur.com/OO4UNqJ
[cookies][info] Extracted 16 cookies from Firefox
./imgur_OO4UNqJ.jpg
real 0m0.456s
user 0m0.183s
sys 0m0.011s
$ gallery-dl --version
1.26.9
```
joskezelensky