Fix autosplat conditions to handle ruby2_keywords case

	Autosplat should not occur if there are two arguments but second
	argument is an array containing a ruby2_keywords splat. Only
	autosplat if a single argument to be yielded to the block, and there
	is no splatted flagged keyword hash passed.

	Fixes [Bug #19759]
	---
	 test/ruby/test_proc.rb | 26 ++++++++++++++++++++++++++
	 vm_args.c              |  3 ++-
	 2 files changed, 28 insertions(+), 1 deletion(-)