fix(passport): apply 409 error handling to sample app ImxRegisterScript

Apply the same 409 error handling fix to the sample app version of
ImxRegisterScript.cs that was previously applied to the Samples~ package
version. The CI tests use the sample app directory, so both files need
the same fix.

Author: rodrigo-fournier-immutable

sample/Assets/Scripts/Passport/ImxRegister/ImxRegisterScript.cs

@@ -43,7 +43,16 @@ public async void RegisterOffchain()
         }
         catch (PassportException e)
         {
-            ShowOutput($"Unable to register off-chain: {e.Message} ({e.Type})");
+            // Handle 409 - account already registered
+            if (e.Type == PassportErrorType.USER_REGISTRATION_ERROR &&
+                (e.Message.Contains("409") || e.Message.Contains("already registered")))
+            {
+                ShowOutput("Passport account already registered");
+            }
+            else
+            {
+                ShowOutput($"Unable to register off-chain: {e.Message} ({e.Type})");
+            }
         }
         catch (Exception e)
         {
@@ -58,4 +67,4 @@ private void ShowOutput(string message)
             Output.text = message;
         }
     }
-}
+}