Avoid getting "index out of range"

Theoretically there is a case when size/base >= len(_map).
I changed the loop's condition expression so there isn't going
to be any bad memory access in the following scenario.

Author: boaz0

size.go

@@ -41,7 +41,8 @@ var binaryAbbrs = []string{"B", "KiB", "MiB", "GiB", "TiB", "PiB", "EiB", "ZiB",
 // using custom format.
 func CustomSize(format string, size float64, base float64, _map []string) string {
 	i := 0
-	for size >= base {
+	unitsLimit := len(_map) - 1
+	for size >= base && i < unitsLimit {
 		size = size / base
 		i++
 	}

size_test.go

@@ -67,6 +67,7 @@ func TestBytesSize(t *testing.T) {
 	assertEquals(t, "3.42 GiB", BytesSize(3.42*GiB))
 	assertEquals(t, "5.372 TiB", BytesSize(5.372*TiB))
 	assertEquals(t, "2.22 PiB", BytesSize(2.22*PiB))
+	assertEquals(t, "1.049e+06 YiB", BytesSize(KiB*KiB*KiB*KiB*KiB*PiB))
 }
 
 func TestHumanSize(t *testing.T) {
@@ -78,6 +79,7 @@ func TestHumanSize(t *testing.T) {
 	assertEquals(t, "3.42 GB", HumanSize(float64(3.42*GB)))
 	assertEquals(t, "5.372 TB", HumanSize(float64(5.372*TB)))
 	assertEquals(t, "2.22 PB", HumanSize(float64(2.22*PB)))
+	assertEquals(t, "1e+04 YB", HumanSize(float64(10000000000000*PB)))
 }
 
 func TestFromHumanSize(t *testing.T) {