This MR fixes bug 428885.
Only local directories were supported to be set as the starting location of Dolphin. This commit fixes this by only checking "fileItem.isDir()" when the path is local because it does not work reliably on remote paths. Additionaly a hard-coded exception for urls with the scheme "timeline" was removed because with the new fix it is now obsolete.
This fix does not check if the URL points to a file when it is on a remote location. Both KDEs KFileItem::isDir() and Qts QFileInfo::isDir() only work for local paths so I'm not sure if a working check would even be possible without getting too verbose. But since it's not possible to select files (only directories) in the selector in the first place and the user would have to enter a path to a file manually, I don't think this is much of a problem.