perf: Skip binary search when timestamp is after last transition

Many zones don't have any future transitions (i.e. all their transitions are in
the past, and they don't have any planned DST changes). For these zones,
looping over the `untils` array is pointless for any "now-ish" timestamp.
If the timestamp being checked is after the last `until`, we can skip the binary
search completely.

moment-timezone.js

@@ -150,16 +150,19 @@
 		}
 	}
 
-	function closest(num, arr) {
+	function closest (num, arr) {
+		var len = arr.length;
 		if (num < arr[0]) {
 			return 0;
-		} else if (num >= arr[arr.length-1]) {
+		} else if (len > 1 && arr[len - 1] === Infinity && num >= arr[len - 2]) {
+			return len - 1;
+		} else if (num >= arr[len - 1]) {
 			return -1;
 		}
 
 		var mid;
 		var lo = 0;
-		var hi = arr.length - 1;  
+		var hi = len - 1;  
 		while (hi - lo > 1) {
 			mid = Math.floor((lo + hi) / 2);
 			if (arr[mid] <= num) {
@@ -185,7 +188,7 @@
 				untils = this.untils,
 				i;
 
-			i = closest(target,untils);
+			i = closest(target, untils);
 			if (i >= 0) {
 				return i;
 			}