installer: suppressed a warning, if the log-rotation-file is created the first time

Author: vogelor

install/lib/installer_base.lib.php

@@ -1413,7 +1413,7 @@ public function install_ispconfig() {
 
 		//* Add Log-Rotation
 		if (is_dir('/etc/logrotate.d')) {
-			unlink('/etc/logrotate.d/logispc3');
+			@unlink('/etc/logrotate.d/logispc3'); // ignore, if the file is not there
 			$fh = fopen('/etc/logrotate.d/logispc3', 'w');
 			fwrite($fh,
 					"/var/log/ispconfig/ispconfig.log { \n" .