patch 8.0.0312: failure when a channel receives a split json message

Problem:    When a json message arrives in pieces, the start is dropped and
            the decoding fails.
Solution:   Do not drop the start when it is still needed. (Kay Zheng)  Add a
            test.  Reset the timeout when something is received.

src/version.c

@@ -764,6 +764,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    312,
 /**/
     311,
 /**/