patch 8.2.3259: when 'indentexpr' causes an error did_throw may hang

Problem:    When 'indentexpr' causes an error the did_throw flag may remain
            set.
Solution:   Reset did_throw and show the error. (closes #8677)
diff --git a/src/proto/ex_docmd.pro b/src/proto/ex_docmd.pro
index 959f209..d22d406 100644
--- a/src/proto/ex_docmd.pro
+++ b/src/proto/ex_docmd.pro
@@ -3,6 +3,7 @@
 int do_cmdline_cmd(char_u *cmd);
 int do_cmd_argument(char_u *cmd);
 int do_cmdline(char_u *cmdline, char_u *(*fgetline)(int, void *, int, getline_opt_T), void *cookie, int flags);
+void handle_did_throw(void);
 int getline_equal(char_u *(*fgetline)(int, void *, int, getline_opt_T), void *cookie, char_u *(*func)(int, void *, int, getline_opt_T));
 void *getline_cookie(char_u *(*fgetline)(int, void *, int, getline_opt_T), void *cookie);
 char_u *getline_peek(char_u *(*fgetline)(int, void *, int, getline_opt_T), void *cookie);