Fix filter not working in zero-copy mode (fixes #1697)

extras/tests/MsgPackDeserializer/filter.cpp

@@ -1027,6 +1027,20 @@ TEST_CASE("deserializeMsgPack() filter") {
   }
 }
 
+TEST_CASE("Zero-copy mode") {  // issue #1697
+  char input[] = "\x82\xA7include\x01\xA6ignore\x02";
+
+  StaticJsonDocument<256> filter;
+  filter["include"] = true;
+
+  StaticJsonDocument<256> doc;
+  DeserializationError err =
+      deserializeMsgPack(doc, input, 18, DeserializationOption::Filter(filter));
+
+  CHECK(err == DeserializationError::Ok);
+  CHECK(doc.as<std::string>() == "{\"include\":1}");
+}
+
 TEST_CASE("Overloads") {
   StaticJsonDocument<256> doc;
   StaticJsonDocument<256> filter;