Add a missing cast to ValueDeserializer::ReadVarint.

src/value-serializer.cc

Index: src/value-serializer.cc
diff --git a/src/value-serializer.cc b/src/value-serializer.cc
index a3e031f7ca587042cc3390e8dc990d584a83fec1..6c3d7e058c2dbf27d35b2b7d2c02ce5faeb55812 100644
--- a/src/value-serializer.cc
+++ b/src/value-serializer.cc
@@ -820,7 +820,7 @@ Maybe<T> ValueDeserializer::ReadVarint() {
     if (position_ >= end_) return Nothing<T>();
     uint8_t byte = *position_;
     if (V8_LIKELY(shift < sizeof(T) * 8)) {
-      value |= (byte & 0x7f) << shift;
+      value |= static_cast<T>(byte & 0x7f) << shift;
       shift += 7;
     }
     has_another_byte = byte & 0x80;