patch 8.2.3961: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move more errors to errors.h.
diff --git a/src/ex_getln.c b/src/ex_getln.c
index 814681b..0be4503 100644
--- a/src/ex_getln.c
+++ b/src/ex_getln.c
@@ -4200,7 +4200,7 @@
     {
 	n = string_to_key(p_cedit, FALSE);
 	if (vim_isprintc(n))
-	    return e_invarg;
+	    return e_invalid_argument;
 	cedit_key = n;
     }
     return NULL;