use try catch to guard against errors in commands

lib/ace/commands/command_manager.js

@@ -33,7 +33,17 @@ oop.inherits(CommandManager, HashHandler);
         if (editor && editor.$readOnly && !command.readOnly)
             return false;
 
-        var retvalue = this._emit("exec", {editor: editor, command: command, args: args});
+        try {
+            var retvalue = this._emit("exec", {
+                editor: editor,
+                command: command,
+                args: args
+            });
+        } catch (e) {
+            window.console && window.console.log(e);
+            return true;
+        }
+
         return retvalue === false ? false : true;
     };