Check if Dolphin already has a handle for stdout or stderr before trying
to attach to the console of the parent process.
Previously, running Dolphin via Git Bash with options like `--help` or
`--version` wouldn't produce any output. This was the result of the fix
(1ce75ce217) for
https://bugs.dolphin-emu.org/issues/11042, before which output did work
for `Git Bash` but didn't for `Command Prompt` or `PowerShell`.