fix warning in hotkey help dialog when disabled hotkey is processed

classes/backend.php

@@ -39,6 +39,7 @@ class Backend extends Handler {
 
 			foreach ($hotkeys as $action => $description) {
 
+				if (is_array($omap[$action])) {
 					foreach ($omap[$action] as $sequence) {
 						if (strpos($sequence, "|") !== FALSE) {
 							$sequence = substr($sequence,
@@ -50,7 +51,7 @@ class Backend extends Handler {
 					 	print "<span class='hksequence'>$sequence</span>";
 					  	print $description;
 						print "</li>";
-
+					}
 				}
 			}
 		}