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/getchar.pro b/src/proto/getchar.pro
index 25aef1c..5f07ad6 100644
--- a/src/proto/getchar.pro
+++ b/src/proto/getchar.pro
@@ -32,7 +32,7 @@
 void del_typebuf(int len, int offset);
 int save_typebuf(void);
 void save_typeahead(tasave_T *tp);
-void restore_typeahead(tasave_T *tp);
+void restore_typeahead(tasave_T *tp, int overwrite);
 void openscript(char_u *name, int directly);
 void close_all_scripts(void);
 int using_script(void);