Fix keyboard event detection in Opera (#1489929)

program/js/common.js

@@ -288,6 +288,7 @@ is_keyboard: function(e)
   return e && (
       (e.pointerType !== undefined && e.pointerType !== 'mouse') ||       // IE 11+
       (e.mozInputSource && e.mozInputSource == e.MOZ_SOURCE_KEYBOARD) ||  // Firefox
+      (e.offsetX === 0 && e.offsetY === 0) || // Opera
       (!e.pageX && (e.pageY || 0) <= 0 && !e.clientX && (e.clientY || 0) <= 0) ||  // others
       (bw.ie && rcube_event._last_keyboard_event && rcube_event._last_keyboard_event.target == e.target)  // hack for IE <= 10
     );