LibPDF: Avoid unnecessary HashMap copy, mark other copies

Author: https://github.com/BenWiederhake
Commit: f866c80222
Pull-request: https://github.com/SerenityOS/serenity/pull/18821
Reviewed-by: https://github.com/awesomekling
Reviewed-by: https://github.com/gmta ✅
Reviewed-by: https://github.com/kleinesfilmroellchen ✅

Userland/Libraries/LibPDF/Encoding.cpp

@@ -43,8 +43,8 @@ PDFErrorOr<NonnullRefPtr<Encoding>> Encoding::from_object(Document* document, No
 
     auto encoding = adopt_ref(*new Encoding());
 
-    encoding->m_descriptors = base_encoding->m_descriptors;
-    encoding->m_name_mapping = base_encoding->m_name_mapping;
+    encoding->m_descriptors = TRY(base_encoding->m_descriptors.clone());
+    encoding->m_name_mapping = TRY(base_encoding->m_name_mapping.clone());
 
     auto differences_array = TRY(dict->get_array(document, CommonNames::Differences));