patch 8.2.4402: missing parenthesis may cause unexpected problems

Problem:    Missing parenthesis may cause unexpected problems.
Solution:   Add more parenthesis is macros. (closes #9788)
diff --git a/src/fileio.c b/src/fileio.c
index 0812462..73fa11b 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -4799,7 +4799,7 @@
 # ifdef FEAT_EVAL
 #  define FREE_ITEM(item)   do { \
 	if (withattr) \
-	    dict_unref((dict_T*)item); \
+	    dict_unref((dict_T*)(item)); \
 	else \
 	    vim_free(item); \
     } while (0)