patch 8.0.0166: JSON with a duplicate key gives an internal error

Problem:    JSON with a duplicate key gives an internal error. (Lcd)
Solution:   Give a normal error.  Avoid an error when parsing JSON from a
            remote client fails.
diff --git a/src/evalfunc.c b/src/evalfunc.c
index f66fa9a..74676c2 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -6818,8 +6818,7 @@
     reader.js_buf = get_tv_string(&argvars[0]);
     reader.js_fill = NULL;
     reader.js_used = 0;
-    if (json_decode_all(&reader, rettv, 0) != OK)
-	EMSG(_(e_invarg));
+    json_decode_all(&reader, rettv, 0);
 }
 
 /*