Fix TTL check

Author: jannikluhn

src/shutter-service/ShutterEventTriggerRegistry.sol

@@ -84,10 +84,11 @@ contract ShutterEventTriggerRegistry is Ownable {
         EventTriggerRegistration storage registrationData = registrations[
             identity
         ];
-        // Ensure no one is trying to decrease ttl.
-        require(registrationData.ttl < ttl, TTLTooShort());
 
         if (registrationData.ttl != 0) {
+            // Ensure no one is trying to decrease ttl.
+            require(registrationData.ttl < ttl, TTLTooShort());
+
             require(
                 keccak256(abi.encode(triggerDefinition)) ==
                     registrationData.triggerDefinitionHash,