patch 8.1.1605: Vim may delay processing messages on a json channel

Problem:    Vim may delay processing messages on a json channel. (Pontus
            Leitzler)
Solution:   Try parsing json when checking if there is readahead.

Author: brammool

src/channel.c

@@ -2851,9 +2851,13 @@ channel_has_readahead(channel_T *channel, ch_part_T part)
     if (ch_mode == MODE_JSON || ch_mode == MODE_JS)
     {
 	jsonq_T   *head = &channel->ch_part[part].ch_json_head;
-	jsonq_T   *item = head->jq_next;
 
-	return item != NULL;
+	if (head->jq_next == NULL)
+	    // Parse json from readahead, there might be a complete message to
+	    // process.
+	    channel_parse_json(channel, part);
+
+	return head->jq_next != NULL;
     }
     return channel_peek(channel, part) != NULL;
 }

src/version.c

@@ -777,6 +777,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1605,
 /**/
     1604,
 /**/