patch 7.4.1261
Problem:    Pending channel messages are garbage collected. Leaking memory in
            ch_sendexpr().  Leaking memory for a decoded JSON string.
Solution:   Mark the message list as used. Free the encoded JSON.  Don't save
            the JSON string.
diff --git a/src/json.c b/src/json.c
index f97d283..b6fce02 100644
--- a/src/json.c
+++ b/src/json.c
@@ -533,10 +533,7 @@
 	if (res != NULL)
 	{
 	    res->v_type = VAR_STRING;
-	    if (ga.ga_data == NULL)
-		res->vval.v_string = NULL;
-	    else
-		res->vval.v_string = vim_strsave(ga.ga_data);
+	    res->vval.v_string = ga.ga_data;
 	}
 	return OK;
     }