handle unknown json::value_t kinds (by aborting)

This should prevent a compile warning when building against nlohmann json.hpp
v3.8.0 or greater, which add an extra value_t kind for binary data.

core/vm.cpp

@@ -1715,6 +1715,14 @@ class Interpreter {
             case json::value_t::discarded: {
                 abort();
             }
+
+            default: {
+                // Newer mlohmann json.hpp (from v3.8.0 https://github.com/nlohmann/json/pull/1662)
+                // add a `value_t::binary` type, used when dealing with some JSON-adjacent binary
+                // formats (BSON, CBOR, etc). Since it doesn't exist prior to v3.8.0 we can't match
+                // on it explicitly, but we can just treat any unknown type as an error.
+                abort();
+            }
         }
     }