Use unsafe_set for more performance

The bounds are already checked at a higher level, so an extra bounds
check is unnecessary overhead.

renderers/gles2/native/stubs.ml

@@ -230,7 +230,7 @@ module Buffer = struct
             arr
 
         let get : t -> int -> float = Bigarray.Array1.unsafe_get
-        let set : t -> int -> float -> unit = Bigarray.Array1.set
+        let set : t -> int -> float -> unit = Bigarray.Array1.unsafe_set
         let length : t -> int  = Bigarray.Array1.dim
         let fill : t -> float -> unit  = Bigarray.Array1.fill
         let blit ~(src : t) ~(s_off : int) ~(dst : t) ~(d_off : int) ~(len : int) : unit =