patch 8.2.4384: Vim9: error message not tested, some code not tested

Problem:    Vim9: error message not tested, some code not tested.
Solution:   Add a couple of test cases.  Give an error for a command modifier
            without a command.
diff --git a/src/errors.h b/src/errors.h
index c5a2649..937c59d 100644
--- a/src/errors.h
+++ b/src/errors.h
@@ -2791,7 +2791,8 @@
 // E1080 unused
 EXTERN char e_cannot_unlet_str[]
 	INIT(= N_("E1081: Cannot unlet %s"));
-// E1082 unused
+EXTERN char e_command_modifier_without_command[]
+	INIT(= N_("E1082: Command modifier without command"));
 EXTERN char e_missing_backtick[]
 	INIT(= N_("E1083: Missing backtick"));
 EXTERN char e_cannot_delete_vim9_script_function_str[]