Fix output path detection to correctly identify directories and files

[CanePlayz]

Related to issue #1502

DiscordChatExporter/DiscordChatExporter.Core/Exporting/ExportRequest.cs

Lines 207 to 220 in acac8f7

	var actualOutputPath = FormatPath(outputPath, guild, channel, after, before);
	// Output is a directory
	if (
	Directory.Exists(actualOutputPath)
	|| string.IsNullOrWhiteSpace(Path.GetExtension(actualOutputPath))
	)
	{
	var fileName = GetDefaultOutputFileName(guild, channel, format, after, before);
	return Path.Combine(actualOutputPath, fileName);
	}
	// Output is a file
	return actualOutputPath;

Issue: You use %G at the end of a path with the guild name containing a period. The heuristic from the code snippet above identifies the resolved server name as a file path as Path.GetExtension(actualOutputPath) does not return Null. DCE then tries to export all channels into this one file, e.g., Discord.Test, leading to a System.IO.IOException due to concurrent access to one file by multiple processes if the export is parallelized.

Solution: Evaluate the extension-based heuristic on the original, unsubstituted outputPath instead of the resolved path. The template path has no unwanted extension and therefore the user intent of creating a directory is preserved.