MethodHandle.asSpreader fix

When the number of arguments to spread is zero, the spreader should be
prepared accept a null arguments array.

Also re-enables test case in LoopCombinatorTest and imports
VarargsArrayTest from OpenJDK 11.0.13.

Bug: 207844518
Test: atest CtsLibcoreOjTestCases:test.java.lang.invoke
Test: atest CtsLibcoreTestCases:libcore.java.lang.invoke
Change-Id: Ie3c3174a7be8f5a87bfaed3f4ee0c5082fb34d35
3 files changed