Lovely picture but I'm pretty sure it's not a Saunder's Gull either! It looks a lot like a Black-headed Gull (Larus ridibundus), although I'm not sure how common those are in Malaysia or what the possible confusion species might be.
I never see this bird before. Whiskered Tern I always see. This bird is twice as big the whiskeredTern. I observed them diving of almost 90 degree down to the sea.
I confuse and do not how to identify this bird for its actual name. After comparing which hopefully will be right, I find that it is more closer to Black-headed Gull. From the color of the feather it indicate it ending its juvenile and molting into winter adult. I study from this site : http://gullpage.tripod.com/gullspage_en/id4.html
I name it as Black-headed Gull and any comment is very much appreciated.
Thanks to all for kind comments especially Bluetail, Andrew whitehouse and a.dancy.