patch 8.2.0909: cannot go back to the previous local directory

Problem:    Cannot go back to the previous local directory.
Solution:   Add "tcd -" and "lcd -". (Yegappan Lakshmanan, closes #4362)

src/filepath.c

@@ -726,6 +726,7 @@ f_chdir(typval_T *argvars, typval_T *rettv)
 
     if (argvars[0].v_type != VAR_STRING)
 	// Returning an empty string means it failed.
+	// No error message, for historic reasons.
 	return;
 
     // Return the current directory