service: Resolve sign conversion errors

These are fairly trivial to resolve and most of the changes entail
using RESULT_UNKNOWN over ResultCode(-1).

src/core/hle/service/bcat/backend/boxcat.cpp

@@ -114,7 +114,7 @@ void HandleDownloadDisplayResult(const AM::Applets::AppletManager& applet_manage
 
     const auto& frontend{applet_manager.GetAppletFrontendSet()};
     frontend.error->ShowCustomErrorText(
-        ResultCode(-1), "There was an error while attempting to use Boxcat.",
+        RESULT_UNKNOWN, "There was an error while attempting to use Boxcat.",
         DOWNLOAD_RESULT_LOG_MESSAGES[static_cast<std::size_t>(res)], [] {});
 }