An AggregateFileSystem in an AggregateFileSystem stomps in TryGetPath

[garrynewman]

In TryGetPath we just return here

zio/src/Zio/FileSystems/AggregateFileSystem.cs

Lines 556 to 559 in 2aa6085

	if (fileSystem is AggregateFileSystem aggregate)
	{
	return aggregate.TryGetPath(path, searchTarget);
	}

But we should really only be returning if the path it returns is valid, since it isn't giving the other systems a chance to check for the file.

[xoofx]

Yep, agreed

[xoofx]

Fixed by commit 8a42485