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.

src/version.c

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