Windows: Fixes subpath symlink evaluation

Paths do not always have Targets, which means that the previously added powershell
command will return an empty string, causing pods with subpath mounts to fail.

pkg/volume/util/subpath/subpath_windows.go

@@ -55,6 +55,10 @@ func evalPath(path string) (linkedPath string, err error) {
 		return "", err
 	}
 	linkedPath = strings.TrimSpace(string(output))
+	if linkedPath == "" {
+		klog.V(4).Infof("Path '%s' has no target. Consiering it as evaluated.", path)
+		return path, nil
+	}
 	if isVolumePrefix(linkedPath) {
 		return path, err
 	}