Fix #122599: Windows Registration/Unregistration Endless Loop

With #120283 the Win32 codepath for registration creates an endless
loop. Command-line arguments are detected for registration that causes
another blender to launch with the same arguments, that repeats
forever. But the only time these arguments is used is when Blender has
already been specifically launched with the permissions needed to
register. So this means it should just do so and then exit.

Pull Request: https://projects.blender.org/blender/blender/pulls/122682

source/creator/creator_args.cc

@@ -1676,17 +1676,26 @@ static int arg_handle_start_with_console(int /*argc*/, const char ** /*argv*/, v
 static bool arg_handle_extension_registration(const bool do_register, const bool all_users)
 {
   /* Logic runs in #main_args_handle_registration. */
+#  ifdef WIN32
+  /* This process has been launched with the permissions needed
+   * to register or unregister, so just do it now and then exit. */
+  if (do_register) {
+    BLI_windows_register_blend_extension(all_users);
+  }
+  else {
+    BLI_windows_unregister_blend_extension(all_users);
+  }
+  TerminateProcess(GetCurrentProcess(), 0);
+  return true;
+#  else
   char *error_msg = nullptr;
   bool result = WM_platform_associate_set(do_register, all_users, &error_msg);
   if (error_msg) {
     fprintf(stderr, "Error: %s\n", error_msg);
     MEM_freeN(error_msg);
   }
-
-#  ifdef WIN32
-  TerminateProcess(GetCurrentProcess(), 0);
-#  endif
   return result;
+#  endif
 }
 
 static const char arg_handle_register_extension_doc[] =