Fix bugs

Author: stevapple

Sources/TSCBasic/Path.swift

@@ -449,18 +449,20 @@ private struct UNIXPath: Path {
 
     var dirname: String {
 #if os(Windows)
-        guard string != "" else {
-            return "."
-        }
         let fsr: UnsafePointer<Int8> = string.fileSystemRepresentation
         defer { fsr.deallocate() }
 
         let path: String = String(cString: fsr)
-        return path.withCString(encodedAs: UTF16.self) {
+        let dir: String = path.withCString(encodedAs: UTF16.self) {
             let data = UnsafeMutaßlePointer(mutating: $0)
             PathCchRemoveFileSpec(data, path.count)
             return String(decodingCString: data, as: UTF16.self)
         }
+        // These two expressions represent for the current directory.
+        if dir == "\\" || dir == "" {
+            return "."
+        }
+        return dir
 #else
         // FIXME: This method seems too complicated; it should be simplified,
         //        if possible, and certainly optimized (using UTF8View).