Fix single mount rename panic

Fixes #12141

hugofs/fileinfo.go

@@ -73,7 +73,9 @@ type FileMeta struct {
 	InclusionFilter *glob.FilenameFilter
 
 	// Rename the name part of the file (not the directory).
-	Rename func(name string, toFrom bool) string
+	// Returns the new name and a boolean indicating if the file
+	// should be included.
+	Rename func(name string, toFrom bool) (string, bool)
 }
 
 func (m *FileMeta) Copy() *FileMeta {