patch 8.2.4010: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move more error messages to errors.h.
diff --git a/src/option.c b/src/option.c
index ef1908f..9cd3031 100644
--- a/src/option.c
+++ b/src/option.c
@@ -1558,7 +1558,7 @@
 		    p = find_termcode(key_name);
 		    if (p == NULL)
 		    {
-			errmsg = N_("E846: Key code not set");
+			errmsg = N_(e_key_code_not_set);
 			goto skip;
 		    }
 		    else