patch 7.4.1238
Problem:    Can't handle two messages right after each other.
Solution:   Find the end of the JSON.  Read more when incomplete.  Add a C
            test for the JSON decoding.
diff --git a/src/eval.c b/src/eval.c
index 01a4512..9a4e1bb 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -14100,9 +14100,9 @@
     js_read_T	reader;
 
     reader.js_buf = get_tv_string(&argvars[0]);
-    reader.js_eof = TRUE;
+    reader.js_fill = NULL;
     reader.js_used = 0;
-    if (json_decode(&reader, rettv) == FAIL)
+    if (json_decode_all(&reader, rettv) != OK)
 	EMSG(_(e_invarg));
 }