fix RID deserialization

Author: Waridley

gdnative-core/src/core_types/rid.rs

@@ -88,7 +88,7 @@ impl PartialOrd for Rid {
 #[cfg(feature = "serde")]
 mod serde {
     use super::*;
-    use ::serde::{de::Visitor, Deserialize, Deserializer, Serialize, Serializer};
+    use ::serde::{de::{Visitor, Error}, Deserialize, Deserializer, Serialize, Serializer};
     use std::fmt::Formatter;
 
     impl Serialize for Rid {
@@ -114,6 +114,13 @@ mod serde {
                 fn expecting(&self, formatter: &mut Formatter) -> std::fmt::Result {
                     formatter.write_str("Unit as an RID placeholder")
                 }
+                
+                fn visit_unit<E>(self) -> Result<Self::Value, E>
+                where
+                  E: Error,
+                {
+                    Ok(Rid::new())
+                }
             }
             deserializer.deserialize_unit(RidVisitor)?;
             Ok(Rid::new())