numeric.c: fix for small number

	* numeric.c (flo_floor, flo_ceil): should not return zero for small
	  number.  [ruby-core:81394] [Bug #13599]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_4@59505 b2dd03c8-39d4-4d8f-98ff-823fe69b080e