Fixed: FS#3131 - Wrong Apache setting for Subdomain (vhost) without hostname

interface/web/sites/lib/lang/en_web_vhost_subdomain.lng

@@ -124,4 +124,5 @@ $wb['variables_txt'] = 'Variables';
 $wb['backup_excludes_txt'] = 'Excluded Directories';
 $wb['backup_excludes_note_txt'] = '(Separate multiple directories with commas. Example: web/cache/*,web/backup)';
 $wb['backup_excludes_error_regex'] = 'The excluded directories contain invalid characters.';
+$wb['subdomain_error_empty'] = 'The subdommain field is empty or contains invalid characters.';
 ?>
\ No newline at end of file

interface/web/sites/web_vhost_subdomain_edit.php

@@ -348,6 +348,11 @@ class page_action extends tform_actions {
 
 		if($app->tform->getCurrentTab() == 'domain') {
 
+			// Check that domain (the subdomain part) is not empty
+			if(!preg_match('/^[a-zA-Z0-9].+/',$this->dataRecord['domain'])) {
+				$app->tform->errorMessage .= $app->tform->lng("subdomain_error_empty")."<br />";
+			}
+			
 			/* check if the domain module is used - and check if the selected domain can be used! */
 			$app->uses('ini_parser,getconf');
 			$settings = $app->getconf->get_global_config('domains');