[horde] Fedora 42 Small Issue - php 8.4.5

[Brent]

After upgrading to Fedora 42, it upgraded php to 8.4.5. It seems there  
is at least one issue where it won't allow a null variable to be used.  
I checked on another system and $app IS null and works fine on 8.3.19.  
It seems php got more stringent on 8.4.5.

In:

<horde-install-dir>/vendor/horde/core/lib/Horde/Registry/Registryconfig.php

 /* Reset textdomain. */
        if ($app != 'horde') {
            textdomain($app);
        }

When you go the the main web url to login, $app is "null". Php won't  
allow you do send a null to the textdomain routine. So,  
"textdomain($app)" throws an error:

A fatal error has occurred
textdomain(): Argument #1 ($domain) must not be empty
in /var/www/horde/vendor/horde/core/lib/Horde/Registry/Registryconfig.php:81

I fixed this by adding the following code just before this section in  
the file shown above. Here's my diff:

@@ -76,6 +76,11 @@
             include $reg_ob->vhost;
         }

+        /* Set app if null */
+        if ($app == '') {
+            $app = 'imp';
+        }
+
         /* Reset textdomain. */
         if ($app != 'horde') {
             textdomain($app);