fix: Wrong query path when saving the layout

[a4lg]

Problem description

At least on Windows (I have tested), it fails to save a layout on the non-portable version of ImHex (unless we have an administrator privilege).

The log (after an attempt to save a layout as "sample") will look like:

Component	Message
libimhex	Failed to save layout 'sample'. No writable path found

But the underlying problem is platform-agnostic. It can be also a problem on other platforms in other ways.

Implementation description

The layout manager incorrectly queried whether the empty path (effectively the current working directory) is writable before saving the layout (not each "layouts" directories it queried earlier).

This is the snippet of the root cause.

std::fs::path layoutPath;
for (const auto &path : hex::fs::getDefaultPaths(fs::ImHexPath::Layouts)) {
    if (!hex::fs::isPathWritable(layoutPath))
        continue;

    layoutPath = path / fileName;
}

Look at the argument we are passing to isPathWritable. layoutPath is a default (empty) std::fs::path object and will not be updated until the directory describing itself is confirmed to be writable.

That caused a problem on non-portable version of Windows because:

1. The current working directory is usually the one of the executable (imhex-gui.exe) and
2. That directory (C:\Program Files\ImHex by default) is usually not writable unless ImHex is executed with an Administrator privilege.

The argument to isPathWritable should be path (containing one of the layouts directories) and this PR fixes so that.

Screenshots

Additional things

This issue is hard to notice when developing because, to reproduce this bug, the current working directory MUST NOT BE writable (usually writable when we develop, even when we are working on the non-portable Windows builds).

[WerWolv]

Thank you!