SI-7080 improve boundary value checking for BitSet

When BitSet accepts a very large integer such as Int.MaxValue,
integer overflow possibly occurs in the calculation of boundary
value "nwords * WordLength". This faulty boundary condition
causes empty-iterator problem like following:

scala> import collection.mutable.BitSet
import collection.mutable.BitSet

scala> val x = BitSet(Int.MaxValue)
x: scala.collection.mutable.BitSet = BitSet()

scala> x.iterator
res0: Iterator[Int] = empty iterator

1 files changed, 14 insertions, 0 deletions

diff --git a/test/files/run/bitsets.scala b/test/files/run/bitsets.scala
index d55f9e4e83..c88782cab7 100644
--- a/test/files/run/bitsets.scala
+++ b/test/files/run/bitsets.scala
@@ -115,6 +115,19 @@ object TestMutable3 {
   println(s"b0:$b0")
 }
 
+object TestMutable4 {
+  import scala.collection.mutable.BitSet
+
+  val bMax = BitSet(Int.MaxValue)
+  println(s"bMax:$bMax")
+  bMax.foreach(println)
+
+  val bLarge = BitSet(2000000001)
+  println(s"bLarge:$bLarge")
+
+  println(bMax == bLarge)
+}
+
 object TestImmutable {
   import scala.collection.immutable.BitSet
 
@@ -190,6 +203,7 @@ object Test extends App {
   TestMutable
   TestMutable2
   TestMutable3
+  TestMutable4
   TestImmutable
   TestImmutable2
 }