fix: exception while deleting empty directories

[Terrails]

SVR_ImportFolder.ImportFolderLocation has a trailing Path.DirectorySeparatorChar like seen here https://github.com/ShokoAnime/ShokoServer/blob/5b016cbce43e0c60bee05138f08671051a3e182b/Shoko.Server/Models/SVR_ImportFolder.cs#L33

Due to those trailing path separators an issue occurs when the the path is passed as directoryToClean to the RecursiveDeleteEmptyDirectories function. The function iterates over all directories in toBeChecked up to directoryToClean and adds any valid paths to directoriesToClean.

So when the function reaches a path equal to directoryToClean it should stop iterating over that tree. The issue is that the path returned by https://github.com/ShokoAnime/ShokoServer/blob/5b016cbce43e0c60bee05138f08671051a3e182b/Shoko.Server/Services/VideoLocal_PlaceService.cs#L497 does not have any trailing path separators. Resulting in the equality check here to be false, even though the two paths are technically equal https://github.com/ShokoAnime/ShokoServer/blob/5b016cbce43e0c60bee05138f08671051a3e182b/Shoko.Server/Services/VideoLocal_PlaceService.cs#L491 This results in a ArgumentOutOfRangeException from the substring it is trying to build due to directoriesToClean being longer with its trailing path separators.

The behaviour can be seen in the following debug window: The function was given ["C:\\shoko\\import\\tsukimichi"] as toBeChecked and "C:\\shoko\\import\\" as directoryToClean. Which obviously results in an exception when it reaches that ternary operator on the 2nd iteration of the while loop.

Simply removing those trailing path separators from directoryToClean fixes this issue on my end.