patch 8.2.4024: confusing error message if imported name is used directly

Problem:    Confusing error message if imported name is used directly.
Solution:   Give a better error message.
diff --git a/src/proto/eval.pro b/src/proto/eval.pro
index f7fa647..ac4a51c 100644
--- a/src/proto/eval.pro
+++ b/src/proto/eval.pro
@@ -70,7 +70,7 @@
 int eval_isnamec(int c);
 int eval_isnamec1(int c);
 int eval_isdictc(int c);
-int handle_subscript(char_u **arg, typval_T *rettv, evalarg_T *evalarg, int verbose);
+int handle_subscript(char_u **arg, char_u *name_start, typval_T *rettv, evalarg_T *evalarg, int verbose);
 int item_copy(typval_T *from, typval_T *to, int deep, int copyID);
 void echo_one(typval_T *rettv, int with_space, int *atstart, int *needclr);
 void ex_echo(exarg_T *eap);