Example of null coalescing assignment operator.

Craig, see if this works. 

$allow_view_other = ( ( $ALLOW_VIEW_OTHER ??= 'Y' ) === 'Y' );

if $ALLOW_VIEW_OTHER is undefined or null, assign 'Y'.
In this case the default from default_config.php. 
Then see if it's === 'Y'

access.php

@@ -23,7 +23,7 @@
  */
 require_once 'includes/init.php';
 
-$allow_view_other = ( $ALLOW_VIEW_OTHER === 'Y' );
+$allow_view_other = ( ( $ALLOW_VIEW_OTHER ??= 'Y' ) === 'Y' );
 
 if( ! access_is_enabled() ) {
   echo print_not_auth();