complex.c: no overflow

	* complex.c (rb_complex_finite_p): get rid of overflow and
	  unnecessary multiplication.

	test_complex.rb: NaN Complex

	* test/ruby/test_complex.rb (test_finite_p): assertions for NaN
	  Complex.  NaN is not an infinite nor a finite number.
	  [ruby-core:83272] [Bug #14014]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_4@62173 b2dd03c8-39d4-4d8f-98ff-823fe69b080e