Fix signed update firmware conversion

retrieveDateTime is a required field, not optional

Signed-off-by: Kai-Uwe Hermann <kai-uwe.hermann@pionix.de>

Author: hikinggrass

modules/OCPP/OCPP.cpp

@@ -577,10 +577,7 @@ void OCPP::ready() {
         firmware_update_request.location = msg.firmware.location;
         firmware_update_request.signature.emplace(msg.firmware.signature.get());
         firmware_update_request.signing_certificate.emplace(msg.firmware.signingCertificate.get());
-
-        if (msg.firmware.retrieveDateTime.has_value()) {
-            firmware_update_request.retrieve_timestamp.emplace(msg.firmware.retrieveDateTime.value().to_rfc3339());
-        }
+        firmware_update_request.retrieve_timestamp.emplace(msg.firmware.retrieveDateTime.to_rfc3339());
 
         if (msg.firmware.installDateTime.has_value()) {
             firmware_update_request.install_timestamp.emplace(msg.firmware.installDateTime.value());