Fix condition where subtraction can overflow

Author: travisbrown

src/library/scala/collection/immutable/Vector.scala

@@ -286,7 +286,7 @@ private sealed abstract class VectorImpl[+A](_prefix1: Arr1) extends Vector[A](_
     val hi = mmin(until, length)
     val newlen = hi - lo
     if(newlen == length) this
-    else if(newlen <= 0) Vector0
+    else if(hi <= lo) Vector0
     else slice0(lo, hi)
   }
 }

test/junit/scala/collection/immutable/VectorTest.scala

@@ -370,6 +370,11 @@ class VectorTest {
     }
   }
 
+  @Test
+  def testSlice3: Unit = {
+    assertEquals(Vector(1).slice(1, -2147483648), Vector())
+  }
+
   @Test
   def testTail: Unit = for(size <- verySmallSizes) {
     var i = 0