patch 8.2.2961: keys typed during a :normal command are discarded

Problem:    Keys typed during a :normal command are discarded.
Solution:   Concatenate saved typeahead and typed kesy. (closes #8340)
diff --git a/src/proto/ui.pro b/src/proto/ui.pro
index e75be32..f44bad1 100644
--- a/src/proto/ui.pro
+++ b/src/proto/ui.pro
@@ -19,7 +19,7 @@
 int vim_free_in_input_buf(void);
 int vim_used_in_input_buf(void);
 char_u *get_input_buf(void);
-void set_input_buf(char_u *p);
+void set_input_buf(char_u *p, int overwrite);
 void add_to_input_buf(char_u *s, int len);
 void add_to_input_buf_csi(char_u *str, int len);
 void trash_input_buf(void);