patch 8.2.4863: accessing freed memory in test without the +channel feature

Problem:    Accessing freed memory in test without the +channel feature.
            (Dominique Pellé)
Solution:   Do not generted PUSHCHANNEL or PUSHJOB if they are not
            implemented. (closes #10350)
diff --git a/src/errors.h b/src/errors.h
index fc815ee..2edbb63 100644
--- a/src/errors.h
+++ b/src/errors.h
@@ -3264,4 +3264,8 @@
 	INIT(= N_("E1275: String or function required for ->(expr)"));
 EXTERN char e_illegal_map_mode_string_str[]
 	INIT(= N_("E1276: Illegal map mode string: '%s'"));
+# if !defined(FEAT_JOB_CHANNEL)
+EXTERN char e_channel_job_feature_not_available[]
+	INIT(= N_("E1277: Channel and job feature is not available"));
+# endif
 #endif